tor-browser

testharness.js (198291B)

---

/*global self*/
/*jshint latedef: nofunc*/

/* Documentation: https://web-platform-tests.org/writing-tests/testharness-api.html
* (../docs/_writing-tests/testharness-api.md) */

(function (global_scope)
{
   // default timeout is 10 seconds, test can override if needed
   var settings = {
       output:true,
       harness_timeout:{
           "normal":10000,
           "long":60000
       },
       test_timeout:null,
       message_events: ["start", "test_state", "result", "completion"],
       debug: false,
   };

   var xhtml_ns = "http://www.w3.org/1999/xhtml";

   /*
    * TestEnvironment is an abstraction for the environment in which the test
    * harness is used. Each implementation of a test environment has to provide
    * the following interface:
    *
    * interface TestEnvironment {
    *   // Invoked after the global 'tests' object has been created and it's
    *   // safe to call add_*_callback() to register event handlers.
    *   void on_tests_ready();
    *
    *   // Invoked after setup() has been called to notify the test environment
    *   // of changes to the test harness properties.
    *   void on_new_harness_properties(object properties);
    *
    *   // Should return a new unique default test name.
    *   DOMString next_default_test_name();
    *
    *   // Should return the test harness timeout duration in milliseconds.
    *   float test_timeout();
    * };
    */

   /*
    * A test environment with a DOM. The global object is 'window'. By default
    * test results are displayed in a table. Any parent windows receive
    * callbacks or messages via postMessage() when test events occur. See
    * apisample11.html and apisample12.html.
    */
   function WindowTestEnvironment() {
       this.name_counter = 0;
       this.window_cache = null;
       this.output_handler = null;
       this.all_loaded = false;
       var this_obj = this;
       this.message_events = [];
       this.dispatched_messages = [];

       this.message_functions = {
           start: [add_start_callback, remove_start_callback,
                   function (properties) {
                       this_obj._dispatch("start_callback", [properties],
                                          {type: "start", properties: properties});
                   }],

           test_state: [add_test_state_callback, remove_test_state_callback,
                        function(test) {
                            this_obj._dispatch("test_state_callback", [test],
                                               {type: "test_state",
                                                test: test.structured_clone()});
                        }],
           result: [add_result_callback, remove_result_callback,
                    function (test) {
                        this_obj.output_handler.show_status();
                        this_obj._dispatch("result_callback", [test],
                                           {type: "result",
                                            test: test.structured_clone()});
                    }],
           completion: [add_completion_callback, remove_completion_callback,
                        function (tests, harness_status, asserts) {
                            var cloned_tests = map(tests, function(test) {
                                return test.structured_clone();
                            });
                            this_obj._dispatch("completion_callback", [tests, harness_status],
                                               {type: "complete",
                                                tests: cloned_tests,
                                                status: harness_status.structured_clone(),
                                                asserts: asserts.map(assert => assert.structured_clone())});
                        }]
       };

       on_event(window, 'load', function() {
         setTimeout(() => {
           this_obj.all_loaded = true;
           if (tests.all_done()) {
             tests.complete();
           }
         },0);
       });

       on_event(window, 'message', function(event) {
           if (event.data && event.data.type === "getmessages" && event.source) {
               // A window can post "getmessages" to receive a duplicate of every
               // message posted by this environment so far. This allows subscribers
               // from fetch_tests_from_window to 'catch up' to the current state of
               // this environment.
               for (var i = 0; i < this_obj.dispatched_messages.length; ++i)
               {
                   event.source.postMessage(this_obj.dispatched_messages[i], "*");
               }
           }
       });
   }

   WindowTestEnvironment.prototype._dispatch = function(selector, callback_args, message_arg) {
       this.dispatched_messages.push(message_arg);
       this._forEach_windows(
               function(w, same_origin) {
                   if (same_origin) {
                       try {
                           var has_selector = selector in w;
                       } catch(e) {
                           // If document.domain was set at some point same_origin can be
                           // wrong and the above will fail.
                           has_selector = false;
                       }
                       if (has_selector) {
                           try {
                               w[selector].apply(undefined, callback_args);
                           } catch (e) {}
                       }
                   }
                   if (w !== self) {
                       w.postMessage(message_arg, "*");
                   }
               });
   };

   WindowTestEnvironment.prototype._forEach_windows = function(callback) {
       // Iterate over the windows [self ... top, opener]. The callback is passed
       // two objects, the first one is the window object itself, the second one
       // is a boolean indicating whether or not it's on the same origin as the
       // current window.
       var cache = this.window_cache;
       if (!cache) {
           cache = [[self, true]];
           var w = self;
           var i = 0;
           var so;
           while (w != w.parent) {
               w = w.parent;
               so = is_same_origin(w);
               cache.push([w, so]);
               i++;
           }
           w = window.opener;
           if (w) {
               cache.push([w, is_same_origin(w)]);
           }
           this.window_cache = cache;
       }

       forEach(cache,
               function(a) {
                   callback.apply(null, a);
               });
   };

   WindowTestEnvironment.prototype.on_tests_ready = function() {
       var output = new Output();
       this.output_handler = output;

       var this_obj = this;

       add_start_callback(function (properties) {
           this_obj.output_handler.init(properties);
       });

       add_test_state_callback(function(test) {
           this_obj.output_handler.show_status();
       });

       add_result_callback(function (test) {
           this_obj.output_handler.show_status();
       });

       add_completion_callback(function (tests, harness_status, asserts_run) {
           this_obj.output_handler.show_results(tests, harness_status, asserts_run);
       });
       this.setup_messages(settings.message_events);
   };

   WindowTestEnvironment.prototype.setup_messages = function(new_events) {
       var this_obj = this;
       forEach(settings.message_events, function(x) {
           var current_dispatch = this_obj.message_events.indexOf(x) !== -1;
           var new_dispatch = new_events.indexOf(x) !== -1;
           if (!current_dispatch && new_dispatch) {
               this_obj.message_functions[x][0](this_obj.message_functions[x][2]);
           } else if (current_dispatch && !new_dispatch) {
               this_obj.message_functions[x][1](this_obj.message_functions[x][2]);
           }
       });
       this.message_events = new_events;
   };

   WindowTestEnvironment.prototype.next_default_test_name = function() {
       var suffix = this.name_counter > 0 ? " " + this.name_counter : "";
       this.name_counter++;
       return get_title() + suffix;
   };

   WindowTestEnvironment.prototype.on_new_harness_properties = function(properties) {
       this.output_handler.setup(properties);
       if (properties.hasOwnProperty("message_events")) {
           this.setup_messages(properties.message_events);
       }
   };

   WindowTestEnvironment.prototype.add_on_loaded_callback = function(callback) {
       on_event(window, 'load', callback);
   };

   WindowTestEnvironment.prototype.test_timeout = function() {
       var metas = document.getElementsByTagName("meta");
       for (var i = 0; i < metas.length; i++) {
           if (metas[i].name === "timeout") {
               if (metas[i].content === "long") {
                   return settings.harness_timeout.long;
               }
               break;
           }
       }
       return settings.harness_timeout.normal;
   };

   /*
    * Base TestEnvironment implementation for a generic web worker.
    *
    * Workers accumulate test results. One or more clients can connect and
    * retrieve results from a worker at any time.
    *
    * WorkerTestEnvironment supports communicating with a client via a
    * MessagePort.  The mechanism for determining the appropriate MessagePort
    * for communicating with a client depends on the type of worker and is
    * implemented by the various specializations of WorkerTestEnvironment
    * below.
    *
    * A client document using testharness can use fetch_tests_from_worker() to
    * retrieve results from a worker. See apisample16.html.
    */
   function WorkerTestEnvironment() {
       this.name_counter = 0;
       this.all_loaded = true;
       this.message_list = [];
       this.message_ports = [];
   }

   WorkerTestEnvironment.prototype._dispatch = function(message) {
       this.message_list.push(message);
       for (var i = 0; i < this.message_ports.length; ++i)
       {
           this.message_ports[i].postMessage(message);
       }
   };

   // The only requirement is that port has a postMessage() method. It doesn't
   // have to be an instance of a MessagePort, and often isn't.
   WorkerTestEnvironment.prototype._add_message_port = function(port) {
       this.message_ports.push(port);
       for (var i = 0; i < this.message_list.length; ++i)
       {
           port.postMessage(this.message_list[i]);
       }
   };

   WorkerTestEnvironment.prototype.next_default_test_name = function() {
       var suffix = this.name_counter > 0 ? " " + this.name_counter : "";
       this.name_counter++;
       return get_title() + suffix;
   };

   WorkerTestEnvironment.prototype.on_new_harness_properties = function() {};

   WorkerTestEnvironment.prototype.on_tests_ready = function() {
       var this_obj = this;
       add_start_callback(
               function(properties) {
                   this_obj._dispatch({
                       type: "start",
                       properties: properties,
                   });
               });
       add_test_state_callback(
               function(test) {
                   this_obj._dispatch({
                       type: "test_state",
                       test: test.structured_clone()
                   });
               });
       add_result_callback(
               function(test) {
                   this_obj._dispatch({
                       type: "result",
                       test: test.structured_clone()
                   });
               });
       add_completion_callback(
               function(tests, harness_status, asserts) {
                   this_obj._dispatch({
                       type: "complete",
                       tests: map(tests,
                           function(test) {
                               return test.structured_clone();
                           }),
                       status: harness_status.structured_clone(),
                       asserts: asserts.map(assert => assert.structured_clone()),
                   });
               });
   };

   WorkerTestEnvironment.prototype.add_on_loaded_callback = function() {};

   WorkerTestEnvironment.prototype.test_timeout = function() {
       // Tests running in a worker don't have a default timeout. I.e. all
       // worker tests behave as if settings.explicit_timeout is true.
       return null;
   };

   /*
    * Dedicated web workers.
    * https://html.spec.whatwg.org/multipage/workers.html#dedicatedworkerglobalscope
    *
    * This class is used as the test_environment when testharness is running
    * inside a dedicated worker.
    */
   function DedicatedWorkerTestEnvironment() {
       WorkerTestEnvironment.call(this);
       // self is an instance of DedicatedWorkerGlobalScope which exposes
       // a postMessage() method for communicating via the message channel
       // established when the worker is created.
       this._add_message_port(self);
   }
   DedicatedWorkerTestEnvironment.prototype = Object.create(WorkerTestEnvironment.prototype);

   DedicatedWorkerTestEnvironment.prototype.on_tests_ready = function() {
       WorkerTestEnvironment.prototype.on_tests_ready.call(this);
       // In the absence of an onload notification, we a require dedicated
       // workers to explicitly signal when the tests are done.
       tests.wait_for_finish = true;
   };

   /*
    * Shared web workers.
    * https://html.spec.whatwg.org/multipage/workers.html#sharedworkerglobalscope
    *
    * This class is used as the test_environment when testharness is running
    * inside a shared web worker.
    */
   function SharedWorkerTestEnvironment() {
       WorkerTestEnvironment.call(this);
       var this_obj = this;
       // Shared workers receive message ports via the 'onconnect' event for
       // each connection.
       self.addEventListener("connect",
               function(message_event) {
                   this_obj._add_message_port(message_event.source);
               }, false);
   }
   SharedWorkerTestEnvironment.prototype = Object.create(WorkerTestEnvironment.prototype);

   SharedWorkerTestEnvironment.prototype.on_tests_ready = function() {
       WorkerTestEnvironment.prototype.on_tests_ready.call(this);
       // In the absence of an onload notification, we a require shared
       // workers to explicitly signal when the tests are done.
       tests.wait_for_finish = true;
   };

   /*
    * Service workers.
    * http://www.w3.org/TR/service-workers/
    *
    * This class is used as the test_environment when testharness is running
    * inside a service worker.
    */
   function ServiceWorkerTestEnvironment() {
       WorkerTestEnvironment.call(this);
       this.all_loaded = false;
       this.on_loaded_callback = null;
       var this_obj = this;
       self.addEventListener("message",
               function(event) {
                   if (event.data && event.data.type && event.data.type === "connect") {
                       this_obj._add_message_port(event.source);
                   }
               }, false);

       // The oninstall event is received after the service worker script and
       // all imported scripts have been fetched and executed. It's the
       // equivalent of an onload event for a document. All tests should have
       // been added by the time this event is received, thus it's not
       // necessary to wait until the onactivate event. However, tests for
       // installed service workers need another event which is equivalent to
       // the onload event because oninstall is fired only on installation. The
       // onmessage event is used for that purpose since tests using
       // testharness.js should ask the result to its service worker by
       // PostMessage. If the onmessage event is triggered on the service
       // worker's context, that means the worker's script has been evaluated.
       on_event(self, "install", on_all_loaded);
       on_event(self, "message", on_all_loaded);
       function on_all_loaded() {
           if (this_obj.all_loaded)
               return;
           this_obj.all_loaded = true;
           if (this_obj.on_loaded_callback) {
             this_obj.on_loaded_callback();
           }
       }
   }

   ServiceWorkerTestEnvironment.prototype = Object.create(WorkerTestEnvironment.prototype);

   ServiceWorkerTestEnvironment.prototype.add_on_loaded_callback = function(callback) {
       if (this.all_loaded) {
           callback();
       } else {
           this.on_loaded_callback = callback;
       }
   };

   /*
    * Shadow realms.
    * https://github.com/tc39/proposal-shadowrealm
    *
    * This class is used as the test_environment when testharness is running
    * inside a shadow realm.
    */
   function ShadowRealmTestEnvironment() {
       WorkerTestEnvironment.call(this);
       this.all_loaded = false;
       this.on_loaded_callback = null;
   }

   ShadowRealmTestEnvironment.prototype = Object.create(WorkerTestEnvironment.prototype);

   /**
    * Signal to the test environment that the tests are ready and the on-loaded
    * callback should be run.
    *
    * Shadow realms are not *really* a DOM context: they have no `onload` or similar
    * event for us to use to set up the test environment; so, instead, this method
    * is manually triggered from the incubating realm
    *
    * @param {Function} message_destination - a function that receives JSON-serializable
    * data to send to the incubating realm, in the same format as used by RemoteContext
    */
   ShadowRealmTestEnvironment.prototype.begin = function(message_destination) {
       if (this.all_loaded) {
           throw new Error("Tried to start a shadow realm test environment after it has already started");
       }
       var fakeMessagePort = {};
       fakeMessagePort.postMessage = message_destination;
       this._add_message_port(fakeMessagePort);
       this.all_loaded = true;
       if (this.on_loaded_callback) {
           this.on_loaded_callback();
       }
   };

   ShadowRealmTestEnvironment.prototype.add_on_loaded_callback = function(callback) {
       if (this.all_loaded) {
           callback();
       } else {
           this.on_loaded_callback = callback;
       }
   };

   /*
    * JavaScript shells.
    *
    * This class is used as the test_environment when testharness is running
    * inside a JavaScript shell.
    */
   function ShellTestEnvironment() {
       this.name_counter = 0;
       this.all_loaded = false;
       this.on_loaded_callback = null;
       Promise.resolve().then(function() {
           this.all_loaded = true;
           if (this.on_loaded_callback) {
               this.on_loaded_callback();
           }
       }.bind(this));
       this.message_list = [];
       this.message_ports = [];
   }

   ShellTestEnvironment.prototype.next_default_test_name = function() {
       var suffix = this.name_counter > 0 ? " " + this.name_counter : "";
       this.name_counter++;
       return get_title() + suffix;
   };

   ShellTestEnvironment.prototype.on_new_harness_properties = function() {};

   ShellTestEnvironment.prototype.on_tests_ready = function() {};

   ShellTestEnvironment.prototype.add_on_loaded_callback = function(callback) {
       if (this.all_loaded) {
           callback();
       } else {
           this.on_loaded_callback = callback;
       }
   };

   ShellTestEnvironment.prototype.test_timeout = function() {
       // Tests running in a shell don't have a default timeout, so behave as
       // if settings.explicit_timeout is true.
       return null;
   };

   function create_test_environment() {
       if ('document' in global_scope) {
           return new WindowTestEnvironment();
       }
       if ('DedicatedWorkerGlobalScope' in global_scope &&
           global_scope instanceof DedicatedWorkerGlobalScope) {
           return new DedicatedWorkerTestEnvironment();
       }
       if ('SharedWorkerGlobalScope' in global_scope &&
           global_scope instanceof SharedWorkerGlobalScope) {
           return new SharedWorkerTestEnvironment();
       }
       if ('ServiceWorkerGlobalScope' in global_scope &&
           global_scope instanceof ServiceWorkerGlobalScope) {
           return new ServiceWorkerTestEnvironment();
       }
       if ('WorkerGlobalScope' in global_scope &&
           global_scope instanceof WorkerGlobalScope) {
           return new DedicatedWorkerTestEnvironment();
       }
       /* Shadow realm global objects are _ordinary_ objects (i.e. their prototype is
        * Object) so we don't have a nice `instanceof` test to use; instead, we
        * check if the there is a GLOBAL.isShadowRealm() property
        * on the global object. that was set by the test harness when it
        * created the ShadowRealm.
        */
       if (global_scope.GLOBAL && global_scope.GLOBAL.isShadowRealm()) {
           return new ShadowRealmTestEnvironment();
       }

       return new ShellTestEnvironment();
   }

   var test_environment = create_test_environment();

   function is_shared_worker(worker) {
       return 'SharedWorker' in global_scope && worker instanceof SharedWorker;
   }

   function is_service_worker(worker) {
       // The worker object may be from another execution context,
       // so do not use instanceof here.
       return 'ServiceWorker' in global_scope &&
           Object.prototype.toString.call(worker) === '[object ServiceWorker]';
   }

   var seen_func_name = Object.create(null);

   function get_test_name(func, name)
   {
       if (name) {
           return name;
       }

       if (func) {
           var func_code = func.toString();

           // Try and match with brackets, but fallback to matching without
           var arrow = func_code.match(/^\(\)\s*=>\s*(?:{(.*)}\s*|(.*))$/);

           // Check for JS line separators
           if (arrow !== null && !/[\u000A\u000D\u2028\u2029]/.test(func_code)) {
               var trimmed = (arrow[1] !== undefined ? arrow[1] : arrow[2]).trim();
               // drop trailing ; if there's no earlier ones
               trimmed = trimmed.replace(/^([^;]*)(;\s*)+$/, "$1");

               if (trimmed) {
                   let name = trimmed;
                   if (seen_func_name[trimmed]) {
                       // This subtest name already exists, so add a suffix.
                       name += " " + seen_func_name[trimmed];
                   } else {
                       seen_func_name[trimmed] = 0;
                   }
                   seen_func_name[trimmed] += 1;
                   return name;
               }
           }
       }

       return test_environment.next_default_test_name();
   }

   /**
    * @callback TestFunction
    * @param {Test} test - The test currnetly being run.
    * @param {Any[]} args - Additional args to pass to function.
    *
    */

   /**
    * Create a synchronous test
    *
    * @param {TestFunction} func - Test function. This is executed
    * immediately. If it returns without error, the test status is
    * set to ``PASS``. If it throws an :js:class:`AssertionError`, or
    * any other exception, the test status is set to ``FAIL``
    * (typically from an `assert` function).
    * @param {String} name - Test name. This must be unique in a
    * given file and must be invariant between runs.
    */
   function test(func, name, properties)
   {
       if (tests.promise_setup_called) {
           tests.status.status = tests.status.ERROR;
           tests.status.message = '`test` invoked after `promise_setup`';
           tests.complete();
       }
       var test_name = get_test_name(func, name);
       var test_obj = new Test(test_name, properties);
       var value = test_obj.step(func, test_obj, test_obj);

       if (value !== undefined) {
           var msg = 'Test named "' + test_name +
               '" passed a function to `test` that returned a value.';

           try {
               if (value && typeof value.then === 'function') {
                   msg += ' Consider using `promise_test` instead when ' +
                       'using Promises or async/await.';
               }
           } catch (err) {}

           tests.status.status = tests.status.ERROR;
           tests.status.message = msg;
       }

       if (test_obj.phase === test_obj.phases.STARTED) {
           test_obj.done();
       }
   }

   /**
    * Create an asynchronous test
    *
    * @param {TestFunction|string} funcOrName - Initial step function
    * to call immediately with the test name as an argument (if any),
    * or name of the test.
    * @param {String} name - Test name (if a test function was
    * provided). This must be unique in a given file and must be
    * invariant between runs.
    * @returns {Test} An object representing the ongoing test.
    */
   function async_test(func, name, properties)
   {
       if (tests.promise_setup_called) {
           tests.status.status = tests.status.ERROR;
           tests.status.message = '`async_test` invoked after `promise_setup`';
           tests.complete();
       }
       if (typeof func !== "function") {
           properties = name;
           name = func;
           func = null;
       }
       var test_name = get_test_name(func, name);
       var test_obj = new Test(test_name, properties);
       if (func) {
           var value = test_obj.step(func, test_obj, test_obj);

           // Test authors sometimes return values to async_test, expecting us
           // to handle the value somehow. Make doing so a harness error to be
           // clear this is invalid, and point authors to promise_test if it
           // may be appropriate.
           //
           // Note that we only perform this check on the initial function
           // passed to async_test, not on any later steps - we haven't seen a
           // consistent problem with those (and it's harder to check).
           if (value !== undefined) {
               var msg = 'Test named "' + test_name +
                   '" passed a function to `async_test` that returned a value.';

               try {
                   if (value && typeof value.then === 'function') {
                       msg += ' Consider using `promise_test` instead when ' +
                           'using Promises or async/await.';
                   }
               } catch (err) {}

               tests.set_status(tests.status.ERROR, msg);
               tests.complete();
           }
       }
       return test_obj;
   }

   /**
    * Create a promise test.
    *
    * Promise tests are tests which are represented by a promise
    * object. If the promise is fulfilled the test passes, if it's
    * rejected the test fails, otherwise the test passes.
    *
    * @param {TestFunction} func - Test function. This must return a
    * promise. The test is automatically marked as complete once the
    * promise settles.
    * @param {String} name - Test name. This must be unique in a
    * given file and must be invariant between runs.
    */
   function promise_test(func, name, properties) {
       if (typeof func !== "function") {
           properties = name;
           name = func;
           func = null;
       }
       var test_name = get_test_name(func, name);
       var test = new Test(test_name, properties);
       test._is_promise_test = true;

       // If there is no promise tests queue make one.
       if (!tests.promise_tests) {
           tests.promise_tests = Promise.resolve();
       }
       tests.promise_tests = tests.promise_tests.then(function() {
           return new Promise(function(resolve) {
               var promise = test.step(func, test, test);

               test.step(function() {
                   assert(!!promise, "promise_test", null,
                          "test body must return a 'thenable' object (received ${value})",
                          {value:promise});
                   assert(typeof promise.then === "function", "promise_test", null,
                          "test body must return a 'thenable' object (received an object with no `then` method)",
                          null);
               });

               // Test authors may use the `step` method within a
               // `promise_test` even though this reflects a mixture of
               // asynchronous control flow paradigms. The "done" callback
               // should be registered prior to the resolution of the
               // user-provided Promise to avoid timeouts in cases where the
               // Promise does not settle but a `step` function has thrown an
               // error.
               add_test_done_callback(test, resolve);

               Promise.resolve(promise)
                   .catch(test.step_func(
                       function(value) {
                           if (value instanceof AssertionError) {
                               throw value;
                           }
                           assert(false, "promise_test", null,
                                  "Unhandled rejection with value: ${value}", {value:value});
                       }))
                   .then(function() {
                       test.done();
                   });
               });
       });
   }

   /**
    * Make a copy of a Promise in the current realm.
    *
    * @param {Promise} promise the given promise that may be from a different
    *                          realm
    * @returns {Promise}
    *
    * An arbitrary promise provided by the caller may have originated
    * in another frame that have since navigated away, rendering the
    * frame's document inactive. Such a promise cannot be used with
    * `await` or Promise.resolve(), as microtasks associated with it
    * may be prevented from being run. See `issue
    * 5319<https://github.com/whatwg/html/issues/5319>`_ for a
    * particular case.
    *
    * In functions we define here, there is an expectation from the caller
    * that the promise is from the current realm, that can always be used with
    * `await`, etc. We therefore create a new promise in this realm that
    * inherit the value and status from the given promise.
    */

   function bring_promise_to_current_realm(promise) {
       return new Promise(promise.then.bind(promise));
   }

   /**
    * Assert that a Promise is rejected with the right ECMAScript exception.
    *
    * @param {Test} test - the `Test` to use for the assertion.
    * @param {Function} constructor - The expected exception constructor.
    * @param {Promise} promise - The promise that's expected to
    * reject with the given exception.
    * @param {string} [description] Error message to add to assert in case of
    *                               failure.
    */
   function promise_rejects_js(test, constructor, promise, description) {
       return bring_promise_to_current_realm(promise)
           .then(test.unreached_func("Should have rejected: " + description))
           .catch(function(e) {
               assert_throws_js_impl(constructor, function() { throw e; },
                                     description, "promise_rejects_js");
           });
   }

   /**
    * Assert that a Promise is rejected with the right DOMException.
    *
    * For the remaining arguments, there are two ways of calling
    * promise_rejects_dom:
    *
    * 1) If the DOMException is expected to come from the current global, the
    * third argument should be the promise expected to reject, and a fourth,
    * optional, argument is the assertion description.
    *
    * 2) If the DOMException is expected to come from some other global, the
    * third argument should be the DOMException constructor from that global,
    * the fourth argument the promise expected to reject, and the fifth,
    * optional, argument the assertion description.
    *
    * @param {Test} test - the `Test` to use for the assertion.
    * @param {number|string} type - See documentation for
    * `assert_throws_dom <#assert_throws_dom>`_.
    * @param {Function} promiseOrConstructor - Either the constructor
    * for the expected exception (if the exception comes from another
    * global), or the promise that's expected to reject (if the
    * exception comes from the current global).
    * @param {Function|string} descriptionOrPromise - Either the
    * promise that's expected to reject (if the exception comes from
    * another global), or the optional description of the condition
    * being tested (if the exception comes from the current global).
    * @param {string} [description] - Description of the condition
    * being tested (if the exception comes from another global).
    *
    */
   function promise_rejects_dom(test, type, promiseOrConstructor, descriptionOrPromise, maybeDescription) {
       let constructor, promise, description;
       if (typeof promiseOrConstructor === "function" &&
           promiseOrConstructor.name === "DOMException") {
           constructor = promiseOrConstructor;
           promise = descriptionOrPromise;
           description = maybeDescription;
       } else {
           constructor = self.DOMException;
           promise = promiseOrConstructor;
           description = descriptionOrPromise;
           assert(maybeDescription === undefined,
                  "Too many args passed to no-constructor version of promise_rejects_dom, or accidentally explicitly passed undefined");
       }
       return bring_promise_to_current_realm(promise)
           .then(test.unreached_func("Should have rejected: " + description))
           .catch(function(e) {
               assert_throws_dom_impl(type, function() { throw e; }, description,
                                      "promise_rejects_dom", constructor);
           });
   }

/**
    * Assert that a `Promise` is rejected with a `QuotaExceededError` with the
    * expected values.
    *
    * For the remaining arguments, there are two ways of calling
    * `promise_rejects_quotaexceedederror`:
    *
    * 1) If the `QuotaExceededError` is expected to come from the
    *    current global, the second argument should be the promise
    *    expected to reject, the third and a fourth the expected
    *    `requested` and `quota` property values, and the fifth,
    *    optional, argument is the assertion description.
    *
    * 2) If the `QuotaExceededError` is expected to come from some
    *    other global, the second argument should be the
    *    `QuotaExceededError` constructor from that global, the third
    *    argument should be the promise expected to reject, the fourth
    *    and fifth the expected `requested` and `quota` property
    *    values, and the sixth, optional, argument is the assertion
    *    description.
    *
    */
   function promise_rejects_quotaexceedederror(test, promiseOrConstructor, requestedOrPromise, quotaOrRequested, descriptionOrQuota, maybeDescription)
   {
       let constructor, promise, requested, quota, description;
       if (typeof promiseOrConstructor === "function" &&
           promiseOrConstructor.name === "QuotaExceededError") {
           constructor = promiseOrConstructor;
           promise = requestedOrPromise;
           requested = quotaOrRequested;
           quota = descriptionOrQuota;
           description = maybeDescription;
       } else {
           constructor = self.QuotaExceededError;
           promise = promiseOrConstructor;
           requested = requestedOrPromise;
           quota = quotaOrRequested;
           description = descriptionOrQuota;
           assert(maybeDescription === undefined,
                  "Too many args passed to no-constructor version of promise_rejects_quotaexceedederror");
       }
       return bring_promise_to_current_realm(promise)
           .then(test.unreached_func("Should have rejected: " + description))
           .catch(function(e) {
               assert_throws_quotaexceedederror_impl(function() { throw e; }, requested, quota, description, "promise_rejects_quotaexceedederror", constructor);
           });
   }

   /**
    * Assert that a Promise is rejected with the provided value.
    *
    * @param {Test} test - the `Test` to use for the assertion.
    * @param {Any} exception - The expected value of the rejected promise.
    * @param {Promise} promise - The promise that's expected to
    * reject.
    * @param {string} [description] Error message to add to assert in case of
    *                               failure.
    */
   function promise_rejects_exactly(test, exception, promise, description) {
       return bring_promise_to_current_realm(promise)
           .then(test.unreached_func("Should have rejected: " + description))
           .catch(function(e) {
               assert_throws_exactly_impl(exception, function() { throw e; },
                                          description, "promise_rejects_exactly");
           });
   }

   /**
    * Allow DOM events to be handled using Promises.
    *
    * This can make it a lot easier to test a very specific series of events,
    * including ensuring that unexpected events are not fired at any point.
    *
    * `EventWatcher` will assert if an event occurs while there is no `wait_for`
    * created Promise waiting to be fulfilled, or if the event is of a different type
    * to the type currently expected. This ensures that only the events that are
    * expected occur, in the correct order, and with the correct timing.
    *
    * @constructor
    * @param {Test} test - The `Test` to use for the assertion.
    * @param {EventTarget} watchedNode - The target expected to receive the events.
    * @param {string[]} eventTypes - List of events to watch for.
    * @param {Promise} timeoutPromise - Promise that will cause the
    * test to be set to `TIMEOUT` once fulfilled.
    *
    */
   function EventWatcher(test, watchedNode, eventTypes, timeoutPromise)
   {
       if (typeof eventTypes === 'string') {
           eventTypes = [eventTypes];
       }

       var waitingFor = null;

       // This is null unless we are recording all events, in which case it
       // will be an Array object.
       var recordedEvents = null;

       var eventHandler = test.step_func(function(evt) {
           assert_true(!!waitingFor,
                       'Not expecting event, but got ' + evt.type + ' event');
           assert_equals(evt.type, waitingFor.types[0],
                         'Expected ' + waitingFor.types[0] + ' event, but got ' +
                         evt.type + ' event instead');

           if (Array.isArray(recordedEvents)) {
               recordedEvents.push(evt);
           }

           if (waitingFor.types.length > 1) {
               // Pop first event from array
               waitingFor.types.shift();
               return;
           }
           // We need to null out waitingFor before calling the resolve function
           // since the Promise's resolve handlers may call wait_for() which will
           // need to set waitingFor.
           var resolveFunc = waitingFor.resolve;
           waitingFor = null;
           // Likewise, we should reset the state of recordedEvents.
           var result = recordedEvents || evt;
           recordedEvents = null;
           resolveFunc(result);
       });

       for (var i = 0; i < eventTypes.length; i++) {
           watchedNode.addEventListener(eventTypes[i], eventHandler, false);
       }

       /**
        * Returns a Promise that will resolve after the specified event or
        * series of events has occurred.
        *
        * @param {Object} options An optional options object. If the 'record' property
        *                 on this object has the value 'all', when the Promise
        *                 returned by this function is resolved,  *all* Event
        *                 objects that were waited for will be returned as an
        *                 array.
        *
        * @example
        * const watcher = new EventWatcher(t, div, [ 'animationstart',
        *                                            'animationiteration',
        *                                            'animationend' ]);
        * return watcher.wait_for([ 'animationstart', 'animationend' ],
        *                         { record: 'all' }).then(evts => {
        *   assert_equals(evts[0].elapsedTime, 0.0);
        *   assert_equals(evts[1].elapsedTime, 2.0);
        * });
        */
       this.wait_for = function(types, options) {
           if (waitingFor) {
               return Promise.reject('Already waiting for an event or events');
           }
           if (typeof types === 'string') {
               types = [types];
           }
           if (options && options.record && options.record === 'all') {
               recordedEvents = [];
           }
           return new Promise(function(resolve, reject) {
               var timeout = test.step_func(function() {
                   // If the timeout fires after the events have been received
                   // or during a subsequent call to wait_for, ignore it.
                   if (!waitingFor || waitingFor.resolve !== resolve)
                       return;

                   // This should always fail, otherwise we should have
                   // resolved the promise.
                   assert_true(waitingFor.types.length === 0,
                               'Timed out waiting for ' + waitingFor.types.join(', '));
                   var result = recordedEvents;
                   recordedEvents = null;
                   var resolveFunc = waitingFor.resolve;
                   waitingFor = null;
                   resolveFunc(result);
               });

               if (timeoutPromise) {
                   timeoutPromise().then(timeout);
               }

               waitingFor = {
                   types: types,
                   resolve: resolve,
                   reject: reject
               };
           });
       };

       /**
        * Stop listening for events
        */
       this.stop_watching = function() {
           for (var i = 0; i < eventTypes.length; i++) {
               watchedNode.removeEventListener(eventTypes[i], eventHandler, false);
           }
       };

       test._add_cleanup(this.stop_watching);

       return this;
   }
   expose(EventWatcher, 'EventWatcher');

   /**
    * @typedef {Object} SettingsObject
    * @property {bool} single_test - Use the single-page-test
    * mode. In this mode the Document represents a single
    * `async_test`. Asserts may be used directly without requiring
    * `Test.step` or similar wrappers, and any exceptions set the
    * status of the test rather than the status of the harness.
    * @property {bool} allow_uncaught_exception - don't treat an
    * uncaught exception as an error; needed when e.g. testing the
    * `window.onerror` handler.
    * @property {boolean} explicit_done - Wait for a call to `done()`
    * before declaring all tests complete (this is always true for
    * single-page tests).
    * @property hide_test_state - hide the test state output while
    * the test is running; This is helpful when the output of the test state
    * may interfere the test results.
    * @property {bool} explicit_timeout - disable file timeout; only
    * stop waiting for results when the `timeout()` function is
    * called This should typically only be set for manual tests, or
    * by a test runner that providees its own timeout mechanism.
    * @property {number} timeout_multiplier - Multiplier to apply to
    * per-test timeouts. This should only be set by a test runner.
    * @property {Document} output_document - The document to which
    * results should be logged. By default this is the current
    * document but could be an ancestor document in some cases e.g. a
    * SVG test loaded in an HTML wrapper
    *
    */

   /**
    * Configure the harness
    *
    * @param {Function|SettingsObject} funcOrProperties - Either a
    * setup function to run, or a set of properties. If this is a
    * function that function is run synchronously. Any exception in
    * the function will set the overall harness status to `ERROR`.
    * @param {SettingsObject} maybeProperties - An object containing
    * the settings to use, if the first argument is a function.
    *
    */
   function setup(func_or_properties, maybe_properties)
   {
       var func = null;
       var properties = {};
       if (arguments.length === 2) {
           func = func_or_properties;
           properties = maybe_properties;
       } else if (func_or_properties instanceof Function) {
           func = func_or_properties;
       } else {
           properties = func_or_properties;
       }
       tests.setup(func, properties);
       test_environment.on_new_harness_properties(properties);
   }

   /**
    * Configure the harness, waiting for a promise to resolve
    * before running any `promise_test` tests.
    *
    * @param {Function} func - Function returning a promise that's
    * run synchronously. Promise tests are not run until after this
    * function has resolved.
    * @param {SettingsObject} [properties] - An object containing
    * the harness settings to use.
    *
    */
   function promise_setup(func, properties={})
   {
       if (typeof func !== "function") {
           tests.set_status(tests.status.ERROR,
                            "`promise_setup` invoked without a function");
           tests.complete();
           return;
       }
       tests.promise_setup_called = true;

       if (!tests.promise_tests) {
           tests.promise_tests = Promise.resolve();
       }

       tests.promise_tests = tests.promise_tests
           .then(function()
                 {
                     var result;

                     tests.setup(null, properties);
                     result = func();
                     test_environment.on_new_harness_properties(properties);

                     if (!result || typeof result.then !== "function") {
                         throw "Non-thenable returned by function passed to `promise_setup`";
                     }
                     return result;
                 })
           .catch(function(e)
                  {
                      tests.set_status(tests.status.ERROR,
                                       String(e),
                                       e && e.stack);
                      tests.complete();
                  });
   }

   /**
    * Mark test loading as complete.
    *
    * Typically this function is called implicitly on page load; it's
    * only necessary for users to call this when either the
    * ``explicit_done`` or ``single_test`` properties have been set
    * via the :js:func:`setup` function.
    *
    * For single page tests this marks the test as complete and sets its status.
    * For other tests, this marks test loading as complete, but doesn't affect ongoing tests.
    */
   function done() {
       if (tests.tests.length === 0) {
           // `done` is invoked after handling uncaught exceptions, so if the
           // harness status is already set, the corresponding message is more
           // descriptive than the generic message defined here.
           if (tests.status.status === null) {
               tests.status.status = tests.status.ERROR;
               tests.status.message = "done() was called without first defining any tests";
           }

           tests.complete();
           return;
       }
       if (tests.file_is_test) {
           // file is test files never have asynchronous cleanup logic,
           // meaning the fully-synchronous `done` function can be used here.
           tests.tests[0].done();
       }
       tests.end_wait();
   }

   /**
    * @deprecated generate a list of tests from a function and list of arguments
    *
    * This is deprecated because it runs all the tests outside of the test functions
    * and as a result any test throwing an exception will result in no tests being
    * run. In almost all cases, you should simply call test within the loop you would
    * use to generate the parameter list array.
    *
    * @param {Function} func - The function that will be called for each generated tests.
    * @param {Any[][]} args - An array of arrays. Each nested array
    * has the structure `[testName, ...testArgs]`. For each of these nested arrays
    * array, a test is generated with name `testName` and test function equivalent to
    * `func(..testArgs)`.
    */
   function generate_tests(func, args, properties) {
       forEach(args, function(x, i)
               {
                   var name = x[0];
                   test(function()
                        {
                            func.apply(this, x.slice(1));
                        },
                        name,
                        Array.isArray(properties) ? properties[i] : properties);
               });
   }

   /**
    * @deprecated
    *
    * Register a function as a DOM event listener to the
    * given object for the event bubbling phase.
    *
    * @param {EventTarget} object - Event target
    * @param {string} event - Event name
    * @param {Function} callback - Event handler.
    */
   function on_event(object, event, callback)
   {
       object.addEventListener(event, callback, false);
   }

   // Internal helper function to provide timeout-like functionality in
   // environments where there is no setTimeout(). (No timeout ID or
   // clearTimeout().)
   function fake_set_timeout(callback, delay) {
       var p = Promise.resolve();
       var start = Date.now();
       var end = start + delay;
       function check() {
           if ((end - Date.now()) > 0) {
               p.then(check);
           } else {
               callback();
           }
       }
       p.then(check);
   }

   /**
    * Global version of :js:func:`Test.step_timeout` for use in single page tests.
    *
    * @param {Function} func - Function to run after the timeout
    * @param {number} timeout - Time in ms to wait before running the
    * test step. The actual wait time is ``timeout`` x
    * ``timeout_multiplier``.
    */
   function step_timeout(func, timeout) {
       var outer_this = this;
       var args = Array.prototype.slice.call(arguments, 2);
       var local_set_timeout = typeof global_scope.setTimeout === "undefined" ? fake_set_timeout : setTimeout;
       return local_set_timeout(function() {
           func.apply(outer_this, args);
       }, timeout * tests.timeout_multiplier);
   }

   expose(test, 'test');
   expose(async_test, 'async_test');
   expose(promise_test, 'promise_test');
   expose(promise_rejects_js, 'promise_rejects_js');
   expose(promise_rejects_dom, 'promise_rejects_dom');
   expose(promise_rejects_quotaexceedederror, 'promise_rejects_quotaexceedederror');
   expose(promise_rejects_exactly, 'promise_rejects_exactly');
   expose(generate_tests, 'generate_tests');
   expose(setup, 'setup');
   expose(promise_setup, 'promise_setup');
   expose(done, 'done');
   expose(on_event, 'on_event');
   expose(step_timeout, 'step_timeout');

   /*
    * Return a string truncated to the given length, with ... added at the end
    * if it was longer.
    */
   function truncate(s, len)
   {
       if (s.length > len) {
           return s.substring(0, len - 3) + "...";
       }
       return s;
   }

   /*
    * Return true if object is probably a Node object.
    */
   function is_node(object)
   {
       // I use duck-typing instead of instanceof, because
       // instanceof doesn't work if the node is from another window (like an
       // iframe's contentWindow):
       // http://www.w3.org/Bugs/Public/show_bug.cgi?id=12295
       try {
           var has_node_properties = ("nodeType" in object &&
                                      "nodeName" in object &&
                                      "nodeValue" in object &&
                                      "childNodes" in object);
       } catch (e) {
           // We're probably cross-origin, which means we aren't a node
           return false;
       }

       if (has_node_properties) {
           try {
               object.nodeType;
           } catch (e) {
               // The object is probably Node.prototype or another prototype
               // object that inherits from it, and not a Node instance.
               return false;
           }
           return true;
       }
       return false;
   }

   var replacements = {
       "0": "0",
       "1": "x01",
       "2": "x02",
       "3": "x03",
       "4": "x04",
       "5": "x05",
       "6": "x06",
       "7": "x07",
       "8": "b",
       "9": "t",
       "10": "n",
       "11": "v",
       "12": "f",
       "13": "r",
       "14": "x0e",
       "15": "x0f",
       "16": "x10",
       "17": "x11",
       "18": "x12",
       "19": "x13",
       "20": "x14",
       "21": "x15",
       "22": "x16",
       "23": "x17",
       "24": "x18",
       "25": "x19",
       "26": "x1a",
       "27": "x1b",
       "28": "x1c",
       "29": "x1d",
       "30": "x1e",
       "31": "x1f",
       "0xfffd": "ufffd",
       "0xfffe": "ufffe",
       "0xffff": "uffff",
   };

   const formatEscapeMap = {
       "\\": "\\\\",
       '"': '\\"'
   };
   for (const p in replacements) {
       formatEscapeMap[String.fromCharCode(p)] = "\\" + replacements[p];
   }
   const formatEscapePattern = new RegExp(`[${Object.keys(formatEscapeMap).map(k => k === "\\" ? "\\\\" : k).join("")}]`, "g");

   /**
    * Convert a value to a nice, human-readable string
    *
    * When many JavaScript Object values are coerced to a String, the
    * resulting value will be ``"[object Object]"``. This obscures
    * helpful information, making the coerced value unsuitable for
    * use in assertion messages, test names, and debugging
    * statements. `format_value` produces more distinctive string
    * representations of many kinds of objects, including arrays and
    * the more important DOM Node types. It also translates String
    * values containing control characters to include human-readable
    * representations.
    *
    * @example
    * // "Document node with 2 children"
    * format_value(document);
    * @example
    * // "\"foo\\uffffbar\""
    * format_value("foo\uffffbar");
    * @example
    * // "[-0, Infinity]"
    * format_value([-0, Infinity]);
    * @param {Any} val - The value to convert to a string.
    * @returns {string} - A string representation of ``val``, optimised for human readability.
    */
   function format_value(val, seen)
   {
       if (!seen) {
           seen = [];
       }
       if (typeof val === "object" && val !== null) {
           if (seen.indexOf(val) >= 0) {
               return "[...]";
           }
           seen.push(val);
       }
       if (Array.isArray(val)) {
           let output = "[";
           if (val.beginEllipsis !== undefined) {
               output += "…, ";
           }
           output += val.map(function(x) {return format_value(x, seen);}).join(", ");
           if (val.endEllipsis !== undefined) {
               output += ", …";
           }
           return output + "]";
       }

       switch (typeof val) {
       case "string":
           return '"' + val.replace(formatEscapePattern, match => formatEscapeMap[match]) + '"';
       case "boolean":
       case "undefined":
           return String(val);
       case "number":
           // In JavaScript, -0 === 0 and String(-0) == "0", so we have to
           // special-case.
           if (val === -0 && 1/val === -Infinity) {
               return "-0";
           }
           return String(val);
       case "bigint":
           return String(val) + 'n';
       case "object":
           if (val === null) {
               return "null";
           }

           // Special-case Node objects, since those come up a lot in my tests.  I
           // ignore namespaces.
           if (is_node(val)) {
               switch (val.nodeType) {
               case Node.ELEMENT_NODE:
                   var ret = "<" + val.localName;
                   for (var i = 0; i < val.attributes.length; i++) {
                       ret += " " + val.attributes[i].name + '="' + val.attributes[i].value + '"';
                   }
                   ret += ">" + val.innerHTML + "</" + val.localName + ">";
                   return "Element node " + truncate(ret, 60);
               case Node.TEXT_NODE:
                   return 'Text node "' + truncate(val.data, 60) + '"';
               case Node.PROCESSING_INSTRUCTION_NODE:
                   return "ProcessingInstruction node with target " + format_value(truncate(val.target, 60)) + " and data " + format_value(truncate(val.data, 60));
               case Node.COMMENT_NODE:
                   return "Comment node <!--" + truncate(val.data, 60) + "-->";
               case Node.DOCUMENT_NODE:
                   return "Document node with " + val.childNodes.length + (val.childNodes.length === 1 ? " child" : " children");
               case Node.DOCUMENT_TYPE_NODE:
                   return "DocumentType node";
               case Node.DOCUMENT_FRAGMENT_NODE:
                   return "DocumentFragment node with " + val.childNodes.length + (val.childNodes.length === 1 ? " child" : " children");
               default:
                   return "Node object of unknown type";
               }
           }

       /* falls through */
       default:
           try {
               return typeof val + ' "' + truncate(String(val), 1000) + '"';
           } catch(e) {
               return ("[stringifying object threw " + String(e) +
                       " with type " + String(typeof e) + "]");
           }
       }
   }
   expose(format_value, "format_value");

   /*
    * Assertions
    */

   function expose_assert(f, name) {
       function assert_wrapper(...args) {
           let status = Test.statuses.TIMEOUT;
           let stack = null;
           let new_assert_index = null;
           try {
               if (settings.debug) {
                   console.debug("ASSERT", name, tests.current_test && tests.current_test.name, args);
               }
               if (tests.output) {
                   tests.set_assert(name, args);
                   // Remember the newly pushed assert's index, because `apply`
                   // below might push new asserts.
                   new_assert_index = tests.asserts_run.length - 1;
               }
               const rv = f.apply(undefined, args);
               status = Test.statuses.PASS;
               return rv;
           } catch(e) {
               status = Test.statuses.FAIL;
               stack = e.stack ? e.stack : null;
               throw e;
           } finally {
               if (tests.output && !stack) {
                   stack = get_stack();
               }
               if (tests.output) {
                   tests.set_assert_status(new_assert_index, status, stack);
               }
           }
       }
       expose(assert_wrapper, name);
   }

   /**
    * Assert that ``actual`` is strictly true
    *
    * @param {Any} actual - Value that is asserted to be true
    * @param {string} [description] - Description of the condition being tested
    */
   function assert_true(actual, description)
   {
       assert(actual === true, "assert_true", description,
                               "expected true got ${actual}", {actual:actual});
   }
   expose_assert(assert_true, "assert_true");

   /**
    * Assert that ``actual`` is strictly false
    *
    * @param {Any} actual - Value that is asserted to be false
    * @param {string} [description] - Description of the condition being tested
    */
   function assert_false(actual, description)
   {
       assert(actual === false, "assert_false", description,
                                "expected false got ${actual}", {actual:actual});
   }
   expose_assert(assert_false, "assert_false");

   function same_value(x, y) {
       if (y !== y) {
           //NaN case
           return x !== x;
       }
       if (x === 0 && y === 0) {
           //Distinguish +0 and -0
           return 1/x === 1/y;
       }
       return x === y;
   }

   /**
    * Assert that ``actual`` is the same value as ``expected``.
    *
    * For objects this compares by object identity; for primitives
    * this distinguishes between 0 and -0, and has correct handling
    * of NaN.
    *
    * @param {Any} actual - Test value.
    * @param {Any} expected - Expected value.
    * @param {string} [description] - Description of the condition being tested.
    */
   function assert_equals(actual, expected, description)
   {
        /*
         * Test if two primitives are equal or two objects
         * are the same object
         */
       if (typeof actual != typeof expected) {
           assert(false, "assert_equals", description,
                         "expected (" + typeof expected + ") ${expected} but got (" + typeof actual + ") ${actual}",
                         {expected:expected, actual:actual});
           return;
       }
       assert(same_value(actual, expected), "assert_equals", description,
                                            "expected ${expected} but got ${actual}",
                                            {expected:expected, actual:actual});
   }
   expose_assert(assert_equals, "assert_equals");

   /**
    * Assert that ``actual`` is not the same value as ``expected``.
    *
    * Comparison is as for :js:func:`assert_equals`.
    *
    * @param {Any} actual - Test value.
    * @param {Any} expected - The value ``actual`` is expected to be different to.
    * @param {string} [description] - Description of the condition being tested.
    */
   function assert_not_equals(actual, expected, description)
   {
       assert(!same_value(actual, expected), "assert_not_equals", description,
                                             "got disallowed value ${actual}",
                                             {actual:actual});
   }
   expose_assert(assert_not_equals, "assert_not_equals");

   /**
    * Assert that ``expected`` is an array and ``actual`` is one of the members.
    * This is implemented using ``indexOf``, so doesn't handle NaN or ±0 correctly.
    *
    * @param {Any} actual - Test value.
    * @param {Array} expected - An array that ``actual`` is expected to
    * be a member of.
    * @param {string} [description] - Description of the condition being tested.
    */
   function assert_in_array(actual, expected, description)
   {
       assert(expected.indexOf(actual) != -1, "assert_in_array", description,
                                              "value ${actual} not in array ${expected}",
                                              {actual:actual, expected:expected});
   }
   expose_assert(assert_in_array, "assert_in_array");

   // This function was deprecated in July of 2015.
   // See https://github.com/web-platform-tests/wpt/issues/2033
   /**
    * @deprecated
    * Recursively compare two objects for equality.
    *
    * See `Issue 2033
    * <https://github.com/web-platform-tests/wpt/issues/2033>`_ for
    * more information.
    *
    * @param {Object} actual - Test value.
    * @param {Object} expected - Expected value.
    * @param {string} [description] - Description of the condition being tested.
    */
   function assert_object_equals(actual, expected, description)
   {
        assert(typeof actual === "object" && actual !== null, "assert_object_equals", description,
                                                              "value is ${actual}, expected object",
                                                              {actual: actual});
        //This needs to be improved a great deal
        function check_equal(actual, expected, stack)
        {
            stack.push(actual);

            var p;
            for (p in actual) {
                assert(expected.hasOwnProperty(p), "assert_object_equals", description,
                                                   "unexpected property ${p}", {p:p});

                if (typeof actual[p] === "object" && actual[p] !== null) {
                    if (stack.indexOf(actual[p]) === -1) {
                        check_equal(actual[p], expected[p], stack);
                    }
                } else {
                    assert(same_value(actual[p], expected[p]), "assert_object_equals", description,
                                                      "property ${p} expected ${expected} got ${actual}",
                                                      {p:p, expected:expected[p], actual:actual[p]});
                }
            }
            for (p in expected) {
                assert(actual.hasOwnProperty(p),
                       "assert_object_equals", description,
                       "expected property ${p} missing", {p:p});
            }
            stack.pop();
        }
        check_equal(actual, expected, []);
   }
   expose_assert(assert_object_equals, "assert_object_equals");

   /**
    * Assert that ``actual`` and ``expected`` are both arrays, and that the array properties of
    * ``actual`` and ``expected`` are all the same value (as for :js:func:`assert_equals`).
    *
    * @param {Array} actual - Test array.
    * @param {Array} expected - Array that is expected to contain the same values as ``actual``.
    * @param {string} [description] - Description of the condition being tested.
    */
   function assert_array_equals(actual, expected, description)
   {
       const max_array_length = 20;
       function shorten_array(arr, offset = 0) {
           // Make ", …" only show up when it would likely reduce the length, not accounting for
           // fonts.
           if (arr.length < max_array_length + 2) {
               return arr;
           }
           // By default we want half the elements after the offset and half before
           // But if that takes us past the end of the array, we have more before, and
           // if it takes us before the start we have more after.
           const length_after_offset = Math.floor(max_array_length / 2);
           let upper_bound = Math.min(length_after_offset + offset, arr.length);
           const lower_bound = Math.max(upper_bound - max_array_length, 0);

           if (lower_bound === 0) {
               upper_bound = max_array_length;
           }

           const output = arr.slice(lower_bound, upper_bound);
           if (lower_bound > 0) {
               output.beginEllipsis = true;
           }
           if (upper_bound < arr.length) {
               output.endEllipsis = true;
           }
           return output;
       }

       assert(typeof actual === "object" && actual !== null && "length" in actual,
              "assert_array_equals", description,
              "value is ${actual}, expected array",
              {actual:actual});
       assert(actual.length === expected.length,
              "assert_array_equals", description,
              "lengths differ, expected array ${expected} length ${expectedLength}, got ${actual} length ${actualLength}",
              {expected:shorten_array(expected, expected.length - 1), expectedLength:expected.length,
               actual:shorten_array(actual, actual.length - 1), actualLength:actual.length
              });

       for (var i = 0; i < actual.length; i++) {
           assert(actual.hasOwnProperty(i) === expected.hasOwnProperty(i),
                  "assert_array_equals", description,
                  "expected property ${i} to be ${expected} but was ${actual} (expected array ${arrayExpected} got ${arrayActual})",
                  {i:i, expected:expected.hasOwnProperty(i) ? "present" : "missing",
                   actual:actual.hasOwnProperty(i) ? "present" : "missing",
                   arrayExpected:shorten_array(expected, i), arrayActual:shorten_array(actual, i)});
           assert(same_value(expected[i], actual[i]),
                  "assert_array_equals", description,
                  "expected property ${i} to be ${expected} but got ${actual} (expected array ${arrayExpected} got ${arrayActual})",
                  {i:i, expected:expected[i], actual:actual[i],
                   arrayExpected:shorten_array(expected, i), arrayActual:shorten_array(actual, i)});
       }
   }
   expose_assert(assert_array_equals, "assert_array_equals");

   /**
    * Assert that each array property in ``actual`` is a number within
    * ± `epsilon` of the corresponding property in `expected`.
    *
    * @param {Array} actual - Array of test values.
    * @param {Array} expected - Array of values expected to be close to the values in ``actual``.
    * @param {number} epsilon - Magnitude of allowed difference
    * between each value in ``actual`` and ``expected``.
    * @param {string} [description] - Description of the condition being tested.
    */
   function assert_array_approx_equals(actual, expected, epsilon, description)
   {
       /*
        * Test if two primitive arrays are equal within +/- epsilon
        */
       assert(actual.length === expected.length,
              "assert_array_approx_equals", description,
              "lengths differ, expected ${expected} got ${actual}",
              {expected:expected.length, actual:actual.length});

       for (var i = 0; i < actual.length; i++) {
           assert(actual.hasOwnProperty(i) === expected.hasOwnProperty(i),
                  "assert_array_approx_equals", description,
                  "property ${i}, property expected to be ${expected} but was ${actual}",
                  {i:i, expected:expected.hasOwnProperty(i) ? "present" : "missing",
                   actual:actual.hasOwnProperty(i) ? "present" : "missing"});
           assert(typeof actual[i] === "number",
                  "assert_array_approx_equals", description,
                  "property ${i}, expected a number but got a ${type_actual}",
                  {i:i, type_actual:typeof actual[i]});
           assert(Math.abs(actual[i] - expected[i]) <= epsilon,
                  "assert_array_approx_equals", description,
                  "property ${i}, expected ${expected} +/- ${epsilon}, expected ${expected} but got ${actual}",
                  {i:i, expected:expected[i], actual:actual[i], epsilon:epsilon});
       }
   }
   expose_assert(assert_array_approx_equals, "assert_array_approx_equals");

   /**
    * Assert that ``actual`` is within ± ``epsilon`` of ``expected``.
    *
    * @param {number} actual - Test value.
    * @param {number} expected - Value number is expected to be close to.
    * @param {number} epsilon - Magnitude of allowed difference between ``actual`` and ``expected``.
    * @param {string} [description] - Description of the condition being tested.
    */
   function assert_approx_equals(actual, expected, epsilon, description)
   {
       /*
        * Test if two primitive numbers are equal within +/- epsilon
        */
       assert(typeof actual === "number",
              "assert_approx_equals", description,
              "expected a number but got a ${type_actual}",
              {type_actual:typeof actual});

       // The epsilon math below does not place nice with NaN and Infinity
       // But in this case Infinity = Infinity and NaN = NaN
       if (isFinite(actual) || isFinite(expected)) {
           assert(Math.abs(actual - expected) <= epsilon,
                  "assert_approx_equals", description,
                  "expected ${expected} +/- ${epsilon} but got ${actual}",
                  {expected:expected, actual:actual, epsilon:epsilon});
       } else {
           assert_equals(actual, expected);
       }
   }
   expose_assert(assert_approx_equals, "assert_approx_equals");

   /**
    * Assert that ``actual`` is a number less than ``expected``.
    *
    * @param {number|bigint} actual - Test value.
    * @param {number|bigint} expected - Value that ``actual`` must be less than.
    * @param {string} [description] - Description of the condition being tested.
    */
   function assert_less_than(actual, expected, description)
   {
       /*
        * Test if a primitive number (or bigint) is less than another
        */
       assert(typeof actual === "number" || typeof actual === "bigint",
              "assert_less_than", description,
              "expected a number but got a ${type_actual}",
              {type_actual:typeof actual});

       assert(typeof actual === typeof expected,
              "assert_less_than", description,
              "expected a ${type_expected} but got a ${type_actual}",
              {type_expected:typeof expected, type_actual:typeof actual});

       assert(actual < expected,
              "assert_less_than", description,
              "expected a number less than ${expected} but got ${actual}",
              {expected:expected, actual:actual});
   }
   expose_assert(assert_less_than, "assert_less_than");

   /**
    * Assert that ``actual`` is a number greater than ``expected``.
    *
    * @param {number|bigint} actual - Test value.
    * @param {number|bigint} expected - Value that ``actual`` must be greater than.
    * @param {string} [description] - Description of the condition being tested.
    */
   function assert_greater_than(actual, expected, description)
   {
       /*
        * Test if a primitive number (or bigint) is greater than another
        */
       assert(typeof actual === "number" || typeof actual === "bigint",
              "assert_greater_than", description,
              "expected a number but got a ${type_actual}",
              {type_actual:typeof actual});

       assert(typeof actual === typeof expected,
              "assert_greater_than", description,
              "expected a ${type_expected} but got a ${type_actual}",
              {type_expected:typeof expected, type_actual:typeof actual});

       assert(actual > expected,
              "assert_greater_than", description,
              "expected a number greater than ${expected} but got ${actual}",
              {expected:expected, actual:actual});
   }
   expose_assert(assert_greater_than, "assert_greater_than");

   /**
    * Assert that ``actual`` is a number greater than ``lower`` and less
    * than ``upper`` but not equal to either.
    *
    * @param {number|bigint} actual - Test value.
    * @param {number|bigint} lower - Value that ``actual`` must be greater than.
    * @param {number|bigint} upper - Value that ``actual`` must be less than.
    * @param {string} [description] - Description of the condition being tested.
    */
   function assert_between_exclusive(actual, lower, upper, description)
   {
       /*
        * Test if a primitive number (or bigint) is between two others
        */
       assert(typeof lower === typeof upper,
              "assert_between_exclusive", description,
              "expected lower (${type_lower}) and upper (${type_upper}) types to match (test error)",
              {type_lower:typeof lower, type_upper:typeof upper});

       assert(typeof actual === "number" || typeof actual === "bigint",
              "assert_between_exclusive", description,
              "expected a number but got a ${type_actual}",
              {type_actual:typeof actual});

       assert(typeof actual === typeof lower,
              "assert_between_exclusive", description,
              "expected a ${type_lower} but got a ${type_actual}",
              {type_lower:typeof lower, type_actual:typeof actual});

       assert(actual > lower && actual < upper,
              "assert_between_exclusive", description,
              "expected a number greater than ${lower} " +
              "and less than ${upper} but got ${actual}",
              {lower:lower, upper:upper, actual:actual});
   }
   expose_assert(assert_between_exclusive, "assert_between_exclusive");

   /**
    * Assert that ``actual`` is a number less than or equal to ``expected``.
    *
    * @param {number|bigint} actual - Test value.
    * @param {number|bigint} expected - Value that ``actual`` must be less
    * than or equal to.
    * @param {string} [description] - Description of the condition being tested.
    */
   function assert_less_than_equal(actual, expected, description)
   {
       /*
        * Test if a primitive number (or bigint) is less than or equal to another
        */
       assert(typeof actual === "number" || typeof actual === "bigint",
              "assert_less_than_equal", description,
              "expected a number but got a ${type_actual}",
              {type_actual:typeof actual});

       assert(typeof actual === typeof expected,
              "assert_less_than_equal", description,
              "expected a ${type_expected} but got a ${type_actual}",
              {type_expected:typeof expected, type_actual:typeof actual});

       assert(actual <= expected,
              "assert_less_than_equal", description,
              "expected a number less than or equal to ${expected} but got ${actual}",
              {expected:expected, actual:actual});
   }
   expose_assert(assert_less_than_equal, "assert_less_than_equal");

   /**
    * Assert that ``actual`` is a number greater than or equal to ``expected``.
    *
    * @param {number|bigint} actual - Test value.
    * @param {number|bigint} expected - Value that ``actual`` must be greater
    * than or equal to.
    * @param {string} [description] - Description of the condition being tested.
    */
   function assert_greater_than_equal(actual, expected, description)
   {
       /*
        * Test if a primitive number (or bigint) is greater than or equal to another
        */
       assert(typeof actual === "number" || typeof actual === "bigint",
              "assert_greater_than_equal", description,
              "expected a number but got a ${type_actual}",
              {type_actual:typeof actual});

       assert(typeof actual === typeof expected,
              "assert_greater_than_equal", description,
              "expected a ${type_expected} but got a ${type_actual}",
              {type_expected:typeof expected, type_actual:typeof actual});

       assert(actual >= expected,
              "assert_greater_than_equal", description,
              "expected a number greater than or equal to ${expected} but got ${actual}",
              {expected:expected, actual:actual});
   }
   expose_assert(assert_greater_than_equal, "assert_greater_than_equal");

   /**
    * Assert that ``actual`` is a number greater than or equal to ``lower`` and less
    * than or equal to ``upper``.
    *
    * @param {number|bigint} actual - Test value.
    * @param {number|bigint} lower - Value that ``actual`` must be greater than or equal to.
    * @param {number|bigint} upper - Value that ``actual`` must be less than or equal to.
    * @param {string} [description] - Description of the condition being tested.
    */
   function assert_between_inclusive(actual, lower, upper, description)
   {
       /*
        * Test if a primitive number (or bigint) is between to two others or equal to either of them
        */
       assert(typeof lower === typeof upper,
              "assert_between_inclusive", description,
              "expected lower (${type_lower}) and upper (${type_upper}) types to match (test error)",
              {type_lower:typeof lower, type_upper:typeof upper});

       assert(typeof actual === "number" || typeof actual === "bigint",
              "assert_between_inclusive", description,
              "expected a number but got a ${type_actual}",
              {type_actual:typeof actual});

       assert(typeof actual === typeof lower,
              "assert_between_inclusive", description,
              "expected a ${type_lower} but got a ${type_actual}",
              {type_lower:typeof lower, type_actual:typeof actual});

       assert(actual >= lower && actual <= upper,
              "assert_between_inclusive", description,
              "expected a number greater than or equal to ${lower} " +
              "and less than or equal to ${upper} but got ${actual}",
              {lower:lower, upper:upper, actual:actual});
   }
   expose_assert(assert_between_inclusive, "assert_between_inclusive");

   /**
    * Assert that ``actual`` matches the RegExp ``expected``.
    *
    * @param {String} actual - Test string.
    * @param {RegExp} expected - RegExp ``actual`` must match.
    * @param {string} [description] - Description of the condition being tested.
    */
   function assert_regexp_match(actual, expected, description) {
       /*
        * Test if a string (actual) matches a regexp (expected)
        */
       assert(expected.test(actual),
              "assert_regexp_match", description,
              "expected ${expected} but got ${actual}",
              {expected:expected, actual:actual});
   }
   expose_assert(assert_regexp_match, "assert_regexp_match");

   /**
    * Assert that the class string of ``object`` as returned in
    * ``Object.prototype.toString`` is equal to ``class_name``.
    *
    * @param {Object} object - Object to stringify.
    * @param {string} class_string - Expected class string for ``object``.
    * @param {string} [description] - Description of the condition being tested.
    */
   function assert_class_string(object, class_string, description) {
       var actual = {}.toString.call(object);
       var expected = "[object " + class_string + "]";
       assert(same_value(actual, expected), "assert_class_string", description,
                                            "expected ${expected} but got ${actual}",
                                            {expected:expected, actual:actual});
   }
   expose_assert(assert_class_string, "assert_class_string");

   /**
    * Assert that ``object`` has an own property with name ``property_name``.
    *
    * @param {Object} object - Object that should have the given property.
    * @param {string} property_name - Expected property name.
    * @param {string} [description] - Description of the condition being tested.
    */
   function assert_own_property(object, property_name, description) {
       assert(object.hasOwnProperty(property_name),
              "assert_own_property", description,
              "expected property ${p} missing", {p:property_name});
   }
   expose_assert(assert_own_property, "assert_own_property");

   /**
    * Assert that ``object`` does not have an own property with name ``property_name``.
    *
    * @param {Object} object - Object that should not have the given property.
    * @param {string} property_name - Property name to test.
    * @param {string} [description] - Description of the condition being tested.
    */
   function assert_not_own_property(object, property_name, description) {
       assert(!object.hasOwnProperty(property_name),
              "assert_not_own_property", description,
              "unexpected property ${p} is found on object", {p:property_name});
   }
   expose_assert(assert_not_own_property, "assert_not_own_property");

   function _assert_inherits(name) {
       return function (object, property_name, description)
       {
           assert((typeof object === "object" && object !== null) ||
                  typeof object === "function" ||
                  // Or has [[IsHTMLDDA]] slot
                  String(object) === "[object HTMLAllCollection]",
                  name, description,
                  "provided value is not an object");

           assert("hasOwnProperty" in object,
                  name, description,
                  "provided value is an object but has no hasOwnProperty method");

           assert(!object.hasOwnProperty(property_name),
                  name, description,
                  "property ${p} found on object expected in prototype chain",
                  {p:property_name});

           assert(property_name in object,
                  name, description,
                  "property ${p} not found in prototype chain",
                  {p:property_name});
       };
   }

   /**
    * Assert that ``object`` does not have an own property with name
    * ``property_name``, but inherits one through the prototype chain.
    *
    * @param {Object} object - Object that should have the given property in its prototype chain.
    * @param {string} property_name - Expected property name.
    * @param {string} [description] - Description of the condition being tested.
    */
   function assert_inherits(object, property_name, description) {
       return _assert_inherits("assert_inherits")(object, property_name, description);
   }
   expose_assert(assert_inherits, "assert_inherits");

   /**
    * Alias for :js:func:`insert_inherits`.
    *
    * @param {Object} object - Object that should have the given property in its prototype chain.
    * @param {string} property_name - Expected property name.
    * @param {string} [description] - Description of the condition being tested.
    */
   function assert_idl_attribute(object, property_name, description) {
       return _assert_inherits("assert_idl_attribute")(object, property_name, description);
   }
   expose_assert(assert_idl_attribute, "assert_idl_attribute");


   /**
    * Assert that ``object`` has a property named ``property_name`` and that the property is not writable or has no setter.
    *
    * @param {Object} object - Object that should have the given (not necessarily own) property.
    * @param {string} property_name - Expected property name.
    * @param {string} [description] - Description of the condition being tested.
    */
   function assert_readonly(object, property_name, description)
   {
       assert(property_name in object,
              "assert_readonly", description,
              "property ${p} not found",
              {p:property_name});

       let desc;
       while (object && (desc = Object.getOwnPropertyDescriptor(object, property_name)) === undefined) {
           object = Object.getPrototypeOf(object);
       }

       assert(desc !== undefined,
              "assert_readonly", description,
              "could not find a descriptor for property ${p}",
              {p:property_name});

       if (desc.hasOwnProperty("value")) {
           // We're a data property descriptor
           assert(desc.writable === false, "assert_readonly", description,
                  "descriptor [[Writable]] expected false got ${actual}", {actual:desc.writable});
       } else if (desc.hasOwnProperty("get") || desc.hasOwnProperty("set")) {
           // We're an accessor property descriptor
           assert(desc.set === undefined, "assert_readonly", description,
                  "property ${p} is an accessor property with a [[Set]] attribute, cannot test readonly-ness",
                  {p:property_name});
       } else {
           // We're a generic property descriptor
           // This shouldn't happen, because Object.getOwnPropertyDescriptor
           // forwards the return value of [[GetOwnProperty]] (P), which must
           // be a fully populated Property Descriptor or Undefined.
           assert(false, "assert_readonly", description,
                  "Object.getOwnPropertyDescriptor must return a fully populated property descriptor");
       }
   }
   expose_assert(assert_readonly, "assert_readonly");

   /**
    * Assert a JS Error with the expected constructor is thrown.
    *
    * @param {object} constructor The expected exception constructor.
    * @param {Function} func Function which should throw.
    * @param {string} [description] Error description for the case that the error is not thrown.
    */
   function assert_throws_js(constructor, func, description)
   {
       assert_throws_js_impl(constructor, func, description,
                             "assert_throws_js");
   }
   expose_assert(assert_throws_js, "assert_throws_js");

   /**
    * Like assert_throws_js but allows specifying the assertion type
    * (assert_throws_js or promise_rejects_js, in practice).
    */
   function assert_throws_js_impl(constructor, func, description,
                                  assertion_type)
   {
       try {
           func.call(this);
           assert(false, assertion_type, description,
                  "${func} did not throw", {func:func});
       } catch (e) {
           if (e instanceof AssertionError) {
               throw e;
           }

           // Basic sanity-checks on the thrown exception.
           assert(typeof e === "object",
                  assertion_type, description,
                  "${func} threw ${e} with type ${type}, not an object",
                  {func:func, e:e, type:typeof e});

           assert(e !== null,
                  assertion_type, description,
                  "${func} threw null, not an object",
                  {func:func});

           // Basic sanity-check on the passed-in constructor
           assert(typeof constructor === "function",
                  assertion_type, description,
                  "${constructor} is not a constructor",
                  {constructor:constructor});
           var obj = constructor;
           while (obj) {
               if (typeof obj === "function" &&
                   obj.name === "Error") {
                   break;
               }
               obj = Object.getPrototypeOf(obj);
           }
           assert(obj != null,
                  assertion_type, description,
                  "${constructor} is not an Error subtype",
                  {constructor:constructor});

           // And checking that our exception is reasonable
           assert(e.constructor === constructor &&
                  e.name === constructor.name,
                  assertion_type, description,
                  "${func} threw ${actual} (${actual_name}) expected instance of ${expected} (${expected_name})",
                  {func:func, actual:e, actual_name:e.name,
                   expected:constructor,
                   expected_name:constructor.name});
       }
   }

   // TODO: Figure out how to document the overloads better.
   // sphinx-js doesn't seem to handle @variation correctly,
   // and only expects a single JSDoc entry per function.
   /**
    * Assert a DOMException with the expected type is thrown.
    *
    * There are two ways of calling assert_throws_dom:
    *
    * 1) If the DOMException is expected to come from the current global, the
    * second argument should be the function expected to throw and a third,
    * optional, argument is the assertion description.
    *
    * 2) If the DOMException is expected to come from some other global, the
    * second argument should be the DOMException constructor from that global,
    * the third argument the function expected to throw, and the fourth, optional,
    * argument the assertion description.
    *
    * @param {number|string} type - The expected exception name or
    * code.  See the `table of names and codes
    * <https://webidl.spec.whatwg.org/#dfn-error-names-table>`_. If a
    * number is passed it should be one of the numeric code values in
    * that table (e.g. 3, 4, etc).  If a string is passed it can
    * either be an exception name (e.g. "HierarchyRequestError",
    * "WrongDocumentError") or the name of the corresponding error
    * code (e.g. "``HIERARCHY_REQUEST_ERR``", "``WRONG_DOCUMENT_ERR``").
    * @param {Function} descriptionOrFunc - The function expected to
    * throw (if the exception comes from another global), or the
    * optional description of the condition being tested (if the
    * exception comes from the current global).
    * @param {string} [description] - Description of the condition
    * being tested (if the exception comes from another global).
    *
    */
   function assert_throws_dom(type, funcOrConstructor, descriptionOrFunc, maybeDescription)
   {
       let constructor, func, description;
       if (funcOrConstructor.name === "DOMException") {
           constructor = funcOrConstructor;
           func = descriptionOrFunc;
           description = maybeDescription;
       } else {
           constructor = self.DOMException;
           func = funcOrConstructor;
           description = descriptionOrFunc;
           assert(maybeDescription === undefined,
                  "Too many args passed to no-constructor version of assert_throws_dom, or accidentally explicitly passed undefined");
       }
       assert_throws_dom_impl(type, func, description, "assert_throws_dom", constructor);
   }
   expose_assert(assert_throws_dom, "assert_throws_dom");

   /**
    * Similar to assert_throws_dom but allows specifying the assertion type
    * (assert_throws_dom or promise_rejects_dom, in practice).  The
    * "constructor" argument must be the DOMException constructor from the
    * global we expect the exception to come from.
    */
   function assert_throws_dom_impl(type, func, description, assertion_type, constructor)
   {
       try {
           func.call(this);
           assert(false, assertion_type, description,
                  "${func} did not throw", {func:func});
       } catch (e) {
           if (e instanceof AssertionError) {
               throw e;
           }

           // Basic sanity-checks on the thrown exception.
           assert(typeof e === "object",
                  assertion_type, description,
                  "${func} threw ${e} with type ${type}, not an object",
                  {func:func, e:e, type:typeof e});

           assert(e !== null,
                  assertion_type, description,
                  "${func} threw null, not an object",
                  {func:func});

           // Sanity-check our type
           assert(typeof type === "number" ||
                  typeof type === "string",
                  assertion_type, description,
                  "${type} is not a number or string",
                  {type:type});

           var codename_name_map = {
               INDEX_SIZE_ERR: 'IndexSizeError',
               HIERARCHY_REQUEST_ERR: 'HierarchyRequestError',
               WRONG_DOCUMENT_ERR: 'WrongDocumentError',
               INVALID_CHARACTER_ERR: 'InvalidCharacterError',
               NO_MODIFICATION_ALLOWED_ERR: 'NoModificationAllowedError',
               NOT_FOUND_ERR: 'NotFoundError',
               NOT_SUPPORTED_ERR: 'NotSupportedError',
               INUSE_ATTRIBUTE_ERR: 'InUseAttributeError',
               INVALID_STATE_ERR: 'InvalidStateError',
               SYNTAX_ERR: 'SyntaxError',
               INVALID_MODIFICATION_ERR: 'InvalidModificationError',
               NAMESPACE_ERR: 'NamespaceError',
               INVALID_ACCESS_ERR: 'InvalidAccessError',
               TYPE_MISMATCH_ERR: 'TypeMismatchError',
               SECURITY_ERR: 'SecurityError',
               NETWORK_ERR: 'NetworkError',
               ABORT_ERR: 'AbortError',
               URL_MISMATCH_ERR: 'URLMismatchError',
               TIMEOUT_ERR: 'TimeoutError',
               INVALID_NODE_TYPE_ERR: 'InvalidNodeTypeError',
               DATA_CLONE_ERR: 'DataCloneError'
           };

           var name_code_map = {
               IndexSizeError: 1,
               HierarchyRequestError: 3,
               WrongDocumentError: 4,
               InvalidCharacterError: 5,
               NoModificationAllowedError: 7,
               NotFoundError: 8,
               NotSupportedError: 9,
               InUseAttributeError: 10,
               InvalidStateError: 11,
               SyntaxError: 12,
               InvalidModificationError: 13,
               NamespaceError: 14,
               InvalidAccessError: 15,
               TypeMismatchError: 17,
               SecurityError: 18,
               NetworkError: 19,
               AbortError: 20,
               URLMismatchError: 21,
               TimeoutError: 23,
               InvalidNodeTypeError: 24,
               DataCloneError: 25,

               EncodingError: 0,
               NotReadableError: 0,
               UnknownError: 0,
               ConstraintError: 0,
               DataError: 0,
               TransactionInactiveError: 0,
               ReadOnlyError: 0,
               VersionError: 0,
               OperationError: 0,
               NotAllowedError: 0,
               OptOutError: 0
           };

           var code_name_map = {};
           for (var key in name_code_map) {
               if (name_code_map[key] > 0) {
                   code_name_map[name_code_map[key]] = key;
               }
           }

           var required_props = {};
           var name;

           if (typeof type === "number") {
               if (type === 0) {
                   throw new AssertionError('Test bug: ambiguous DOMException code 0 passed to assert_throws_dom()');
               }
               if (type === 22) {
                   throw new AssertionError('Test bug: QuotaExceededError needs to be tested for using assert_throws_quotaexceedederror()');
               }
               if (!(type in code_name_map)) {
                   throw new AssertionError('Test bug: unrecognized DOMException code "' + type + '" passed to assert_throws_dom()');
               }
               name = code_name_map[type];
               required_props.code = type;
           } else if (typeof type === "string") {
               if (name === "QuotaExceededError") {
                   throw new AssertionError('Test bug: QuotaExceededError needs to be tested for using assert_throws_quotaexceedederror()');
               }
               name = type in codename_name_map ? codename_name_map[type] : type;
               if (!(name in name_code_map)) {
                   throw new AssertionError('Test bug: unrecognized DOMException code name or name "' + type + '" passed to assert_throws_dom()');
               }

               required_props.code = name_code_map[name];
           }

           if (required_props.code === 0 ||
              ("name" in e &&
               e.name !== e.name.toUpperCase() &&
               e.name !== "DOMException")) {
               // New style exception: also test the name property.
               required_props.name = name;
           }

           for (var prop in required_props) {
               assert(prop in e && e[prop] == required_props[prop],
                      assertion_type, description,
                      "${func} threw ${e} that is not a DOMException " + type + ": property ${prop} is equal to ${actual}, expected ${expected}",
                      {func:func, e:e, prop:prop, actual:e[prop], expected:required_props[prop]});
           }

           // Check that the exception is from the right global.  This check is last
           // so more specific, and more informative, checks on the properties can
           // happen in case a totally incorrect exception is thrown.
           assert(e.constructor === constructor,
                  assertion_type, description,
                  "${func} threw an exception from the wrong global",
                  {func});

       }
   }

   /**
    * Assert a `QuotaExceededError` with the expected values is thrown.
    *
    * There are two ways of calling `assert_throws_quotaexceedederror`:
    *
    * 1) If the `QuotaExceededError` is expected to come from the
    *    current global, the first argument should be the function
    *    expected to throw, the second and a third the expected
    *    `requested` and `quota` property values, and the fourth,
    *    optional, argument is the assertion description.
    *
    * 2) If the `QuotaExceededError` is expected to come from some
    *    other global, the first argument should be the
    *    `QuotaExceededError` constructor from that global, the second
    *    argument should be the function expected to throw, the third
    *    and fourth the expected `requested` and `quota` property
    *    values, and the fifth, optional, argument is the assertion
    *    description.
    *
    * For the `requested` and `quota` values, instead of `null` or a
    * number, the caller can provide a function which determines
    * whether the value is acceptable by returning a boolean.
    *
    */
   function assert_throws_quotaexceedederror(funcOrConstructor, requestedOrFunc, quotaOrRequested, descriptionOrQuota, maybeDescription)
   {
       let constructor, func, requested, quota, description;
       if (funcOrConstructor.name === "QuotaExceededError") {
           constructor = funcOrConstructor;
           func = requestedOrFunc;
           requested = quotaOrRequested;
           quota = descriptionOrQuota;
           description = maybeDescription;
       } else {
           constructor = self.QuotaExceededError;
           func = funcOrConstructor;
           requested = requestedOrFunc;
           quota = quotaOrRequested;
           description = descriptionOrQuota;
           assert(maybeDescription === undefined,
                  "Too many args passed to no-constructor version of assert_throws_quotaexceedederror");
       }
       assert_throws_quotaexceedederror_impl(func, requested, quota, description, "assert_throws_quotaexceedederror", constructor);
   }
   expose_assert(assert_throws_quotaexceedederror, "assert_throws_quotaexceedederror");

   /**
    * Similar to `assert_throws_quotaexceedederror` but allows
    * specifying the assertion type
    * (`"assert_throws_quotaexceedederror"` or
    * `"promise_rejects_quotaexceedederror"`, in practice). The
    * `constructor` argument must be the `QuotaExceededError`
    * constructor from the global we expect the exception to come from.
    */
   function assert_throws_quotaexceedederror_impl(func, requested, quota, description, assertion_type, constructor)
   {
       try {
           func.call(this);
           assert(false, assertion_type, description, "${func} did not throw",
                  {func});
       } catch (e) {
           if (e instanceof AssertionError) {
               throw e;
           }

           // Basic sanity-checks on the thrown exception.
           assert(typeof e === "object",
                  assertion_type, description,
                  "${func} threw ${e} with type ${type}, not an object",
                  {func, e, type:typeof e});

           assert(e !== null,
                  assertion_type, description,
                  "${func} threw null, not an object",
                  {func});

           // Sanity-check our requested and quota.
           assert(requested === null ||
                  typeof requested === "number" ||
                  typeof requested === "function",
                  assertion_type, description,
                  "${requested} is not null, a number, or a function",
                  {requested});
           assert(quota === null ||
                  typeof quota === "number" ||
                  typeof quota === "function",
                  assertion_type, description,
                  "${quota} is not null or a number",
                  {quota});

           const required_props = {
               code: 22,
               name: "QuotaExceededError"
           };
           if (typeof requested !== "function") {
               required_props.requested = requested;
           }
           if (typeof quota !== "function") {
               required_props.quota = quota;
           }

           for (const [prop, expected] of Object.entries(required_props)) {
               assert(prop in e && e[prop] == expected,
                      assertion_type, description,
                      "${func} threw ${e} that is not a correct QuotaExceededError: property ${prop} is equal to ${actual}, expected ${expected}",
                      {func, e, prop, actual:e[prop], expected});
           }

           if (typeof requested === "function") {
               assert(requested(e.requested),
                      assertion_type, description,
                      "${func} threw ${e} that is not a correct QuotaExceededError: requested value ${requested} did not pass the requested predicate",
                      {func, e, requested});
           }
           if (typeof quota === "function") {
               assert(quota(e.quota),
                      assertion_type, description,
                      "${func} threw ${e} that is not a correct QuotaExceededError: quota value ${quota} did not pass the quota predicate",
                      {func, e, quota});
           }

           // Check that the exception is from the right global.  This check is last
           // so more specific, and more informative, checks on the properties can
           // happen in case a totally incorrect exception is thrown.
           assert(e.constructor === constructor,
                  assertion_type, description,
                  "${func} threw an exception from the wrong global",
                  {func});
       }
   }

   /**
    * Assert the provided value is thrown.
    *
    * @param {value} exception The expected exception.
    * @param {Function} func Function which should throw.
    * @param {string} [description] Error description for the case that the error is not thrown.
    */
   function assert_throws_exactly(exception, func, description)
   {
       assert_throws_exactly_impl(exception, func, description,
                                  "assert_throws_exactly");
   }
   expose_assert(assert_throws_exactly, "assert_throws_exactly");

   /**
    * Like assert_throws_exactly but allows specifying the assertion type
    * (assert_throws_exactly or promise_rejects_exactly, in practice).
    */
   function assert_throws_exactly_impl(exception, func, description,
                                       assertion_type)
   {
       try {
           func.call(this);
           assert(false, assertion_type, description,
                  "${func} did not throw", {func:func});
       } catch (e) {
           if (e instanceof AssertionError) {
               throw e;
           }

           assert(same_value(e, exception), assertion_type, description,
                  "${func} threw ${e} but we expected it to throw ${exception}",
                  {func:func, e:e, exception:exception});
       }
   }

   /**
    * Asserts if called. Used to ensure that a specific codepath is
    * not taken e.g. that an error event isn't fired.
    *
    * @param {string} [description] - Description of the condition being tested.
    */
   function assert_unreached(description) {
        assert(false, "assert_unreached", description,
               "Reached unreachable code");
   }
   expose_assert(assert_unreached, "assert_unreached");

   /**
    * @callback AssertFunc
    * @param {Any} actual
    * @param {Any} expected
    * @param {Any[]} args
    */

   /**
    * Asserts that ``actual`` matches at least one value of ``expected``
    * according to a comparison defined by ``assert_func``.
    *
    * Note that tests with multiple allowed pass conditions are bad
    * practice unless the spec specifically allows multiple
    * behaviours. Test authors should not use this method simply to
    * hide UA bugs.
    *
    * @param {AssertFunc} assert_func - Function to compare actual
    * and expected. It must throw when the comparison fails and
    * return when the comparison passes.
    * @param {Any} actual - Test value.
    * @param {Array} expected_array - Array of possible expected values.
    * @param {Any[]} args - Additional arguments to pass to ``assert_func``.
    */
   function assert_any(assert_func, actual, expected_array, ...args)
   {
       var errors = [];
       var passed = false;
       forEach(expected_array,
               function(expected)
               {
                   try {
                       assert_func.apply(this, [actual, expected].concat(args));
                       passed = true;
                   } catch (e) {
                       errors.push(e.message);
                   }
               });
       if (!passed) {
           throw new AssertionError(errors.join("\n\n"));
       }
   }
   // FIXME: assert_any cannot use expose_assert, because assert_wrapper does
   // not support nested assert calls (e.g. to assert_func). We need to
   // support bypassing assert_wrapper for the inner asserts here.
   expose(assert_any, "assert_any");

   /**
    * Assert that a feature is implemented, based on a 'truthy' condition.
    *
    * This function should be used to early-exit from tests in which there is
    * no point continuing without support for a non-optional spec or spec
    * feature. For example:
    *
    *     assert_implements(window.Foo, 'Foo is not supported');
    *
    * @param {object} condition The truthy value to test
    * @param {string} [description] Error description for the case that the condition is not truthy.
    */
   function assert_implements(condition, description) {
       assert(!!condition, "assert_implements", description);
   }
   expose_assert(assert_implements, "assert_implements");

   /**
    * Assert that an optional feature is implemented, based on a 'truthy' condition.
    *
    * This function should be used to early-exit from tests in which there is
    * no point continuing without support for an explicitly optional spec or
    * spec feature. For example:
    *
    *     assert_implements_optional(video.canPlayType("video/webm"),
    *                                "webm video playback not supported");
    *
    * @param {object} condition The truthy value to test
    * @param {string} [description] Error description for the case that the condition is not truthy.
    */
   function assert_implements_optional(condition, description) {
       if (!condition) {
           throw new OptionalFeatureUnsupportedError(description);
       }
   }
   expose_assert(assert_implements_optional, "assert_implements_optional");

   /**
    * @class
    *
    * A single subtest. A Test is not constructed directly but via the
    * :js:func:`test`, :js:func:`async_test` or :js:func:`promise_test` functions.
    *
    * @param {string} name - This must be unique in a given file and must be
    * invariant between runs.
    *
    */
   function Test(name, properties)
   {
       if (tests.file_is_test && tests.tests.length) {
           throw new Error("Tried to create a test with file_is_test");
       }
       /** The test name. */
       this.name = name;

       this.phase = (tests.is_aborted || tests.phase === tests.phases.COMPLETE) ?
           this.phases.COMPLETE : this.phases.INITIAL;

       /** The test status code.*/
       this.status = this.NOTRUN;
       this.timeout_id = null;
       this.index = null;

       this.properties = properties || {};
       this.timeout_length = settings.test_timeout;
       if (this.timeout_length !== null) {
           this.timeout_length *= tests.timeout_multiplier;
       }

       /** A message indicating the reason for test failure. */
       this.message = null;
       /** Stack trace in case of failure. */
       this.stack = null;

       this.steps = [];
       this._is_promise_test = false;

       this.cleanup_callbacks = [];
       this._user_defined_cleanup_count = 0;
       this._done_callbacks = [];

       if (typeof AbortController === "function") {
           this._abortController = new AbortController();
       }

       // Tests declared following harness completion are likely an indication
       // of a programming error, but they cannot be reported
       // deterministically.
       if (tests.phase === tests.phases.COMPLETE) {
           return;
       }

       tests.push(this);
   }

   /**
    * Enum of possible test statuses.
    *
    * :values:
    *   - ``PASS``
    *   - ``FAIL``
    *   - ``TIMEOUT``
    *   - ``NOTRUN``
    *   - ``PRECONDITION_FAILED``
    */
   Test.statuses = {
       PASS:0,
       FAIL:1,
       TIMEOUT:2,
       NOTRUN:3,
       PRECONDITION_FAILED:4
   };

   Test.prototype = merge({}, Test.statuses);

   Test.prototype.phases = {
       INITIAL:0,
       STARTED:1,
       HAS_RESULT:2,
       CLEANING:3,
       COMPLETE:4
   };

   Test.prototype.status_formats = {
       0: "Pass",
       1: "Fail",
       2: "Timeout",
       3: "Not Run",
       4: "Optional Feature Unsupported",
   };

   Test.prototype.format_status = function() {
       return this.status_formats[this.status];
   };

   Test.prototype.structured_clone = function()
   {
       if (!this._structured_clone) {
           var msg = this.message;
           msg = msg ? String(msg) : msg;
           this._structured_clone = merge({
               name:String(this.name),
               properties:merge({}, this.properties),
               phases:merge({}, this.phases)
           }, Test.statuses);
       }
       this._structured_clone.status = this.status;
       this._structured_clone.message = this.message;
       this._structured_clone.stack = this.stack;
       this._structured_clone.index = this.index;
       this._structured_clone.phase = this.phase;
       return this._structured_clone;
   };

   /**
    * Run a single step of an ongoing test.
    *
    * @param {string} func - Callback function to run as a step. If
    * this throws an :js:func:`AssertionError`, or any other
    * exception, the :js:class:`Test` status is set to ``FAIL``.
    * @param {Object} [this_obj] - The object to use as the this
    * value when calling ``func``. Defaults to the  :js:class:`Test` object.
    */
   Test.prototype.step = function(func, this_obj)
   {
       if (this.phase > this.phases.STARTED) {
           return;
       }

       if (settings.debug && this.phase !== this.phases.STARTED) {
           console.log("TEST START", this.name);
       }
       this.phase = this.phases.STARTED;
       //If we don't get a result before the harness times out that will be a test timeout
       this.set_status(this.TIMEOUT, "Test timed out");

       tests.started = true;
       tests.current_test = this;
       tests.notify_test_state(this);

       if (this.timeout_id === null) {
           this.set_timeout();
       }

       this.steps.push(func);

       if (arguments.length === 1) {
           this_obj = this;
       }

       if (settings.debug) {
           console.debug("TEST STEP", this.name);
       }

       try {
           return func.apply(this_obj, Array.prototype.slice.call(arguments, 2));
       } catch (e) {
           if (this.phase >= this.phases.HAS_RESULT) {
               return;
           }
           var status = e instanceof OptionalFeatureUnsupportedError ? this.PRECONDITION_FAILED : this.FAIL;
           var message = String((typeof e === "object" && e !== null) ? e.message : e);
           var stack = e.stack ? e.stack : null;

           this.set_status(status, message, stack);
           this.phase = this.phases.HAS_RESULT;
           this.done();
       } finally {
           this.current_test = null;
       }
   };

   /**
    * Wrap a function so that it runs as a step of the current test.
    *
    * This allows creating a callback function that will run as a
    * test step.
    *
    * @example
    * let t = async_test("Example");
    * onload = t.step_func(e => {
    *   assert_equals(e.name, "load");
    *   // Mark the test as complete.
    *   t.done();
    * })
    *
    * @param {string} func - Function to run as a step. If this
    * throws an :js:func:`AssertionError`, or any other exception,
    * the :js:class:`Test` status is set to ``FAIL``.
    * @param {Object} [this_obj] - The object to use as the this
    * value when calling ``func``. Defaults to the :js:class:`Test` object.
    */
   Test.prototype.step_func = function(func, this_obj)
   {
       var test_this = this;

       if (arguments.length === 1) {
           this_obj = test_this;
       }

       return function()
       {
           return test_this.step.apply(test_this, [func, this_obj].concat(
               Array.prototype.slice.call(arguments)));
       };
   };

   /**
    * Wrap a function so that it runs as a step of the current test,
    * and automatically marks the test as complete if the function
    * returns without error.
    *
    * @param {string} func - Function to run as a step. If this
    * throws an :js:func:`AssertionError`, or any other exception,
    * the :js:class:`Test` status is set to ``FAIL``. If it returns
    * without error the status is set to ``PASS``.
    * @param {Object} [this_obj] - The object to use as the this
    * value when calling `func`. Defaults to the :js:class:`Test` object.
    */
   Test.prototype.step_func_done = function(func, this_obj)
   {
       var test_this = this;

       if (arguments.length === 1) {
           this_obj = test_this;
       }

       return function()
       {
           if (func) {
               test_this.step.apply(test_this, [func, this_obj].concat(
                   Array.prototype.slice.call(arguments)));
           }
           test_this.done();
       };
   };

   /**
    * Return a function that automatically sets the current test to
    * ``FAIL`` if it's called.
    *
    * @param {string} [description] - Error message to add to assert
    * in case of failure.
    *
    */
   Test.prototype.unreached_func = function(description)
   {
       return this.step_func(function() {
           assert_unreached(description);
       });
   };

   /**
    * Run a function as a step of the test after a given timeout.
    *
    * This multiplies the timeout by the global timeout multiplier to
    * account for the expected execution speed of the current test
    * environment. For example ``test.step_timeout(f, 2000)`` with a
    * timeout multiplier of 2 will wait for 4000ms before calling ``f``.
    *
    * In general it's encouraged to use :js:func:`Test.step_wait` or
    * :js:func:`step_wait_func` in preference to this function where possible,
    * as they provide better test performance.
    *
    * @param {Function} func - Function to run as a test
    * step.
    * @param {number} timeout - Time in ms to wait before running the
    * test step. The actual wait time is ``timeout`` x
    * ``timeout_multiplier``.
    *
    */
   Test.prototype.step_timeout = function(func, timeout) {
       var test_this = this;
       var args = Array.prototype.slice.call(arguments, 2);
       var local_set_timeout = typeof global_scope.setTimeout === "undefined" ? fake_set_timeout : setTimeout;
       return local_set_timeout(this.step_func(function() {
           return func.apply(test_this, args);
       }), timeout * tests.timeout_multiplier);
   };

   /**
    * Poll for a function to return true, and call a callback
    * function once it does, or assert if a timeout is
    * reached. This is preferred over a simple step_timeout
    * whenever possible since it allows the timeout to be longer
    * to reduce intermittents without compromising test execution
    * speed when the condition is quickly met.
    *
    * @param {Function} cond A function taking no arguments and
    *                        returning a boolean or a Promise. The callback is
    *                        called when this function returns true, or the
    *                        returned Promise is resolved with true.
    * @param {Function} func A function taking no arguments to call once
    *                        the condition is met.
    * @param {string} [description] Error message to add to assert in case of
    *                               failure.
    * @param {number} timeout Timeout in ms. This is multiplied by the global
    *                         timeout_multiplier
    * @param {number} interval Polling interval in ms
    *
    */
   Test.prototype.step_wait_func = function(cond, func, description,
                                            timeout=3000, interval=100) {
       var timeout_full = timeout * tests.timeout_multiplier;
       var remaining = Math.ceil(timeout_full / interval);
       var test_this = this;
       var local_set_timeout = typeof global_scope.setTimeout === 'undefined' ? fake_set_timeout : setTimeout;

       const step = test_this.step_func((result) => {
           if (result) {
               func();
           } else {
               if (remaining === 0) {
                   assert(false, "step_wait_func", description,
                          "Timed out waiting on condition");
               }
               remaining--;
               local_set_timeout(wait_for_inner, interval);
           }
       });

       var wait_for_inner = test_this.step_func(() => {
           Promise.resolve(cond()).then(
               step,
               test_this.unreached_func("step_wait_func"));
       });

       wait_for_inner();
   };

   /**
    * Poll for a function to return true, and invoke a callback
    * followed by this.done() once it does, or assert if a timeout
    * is reached. This is preferred over a simple step_timeout
    * whenever possible since it allows the timeout to be longer
    * to reduce intermittents without compromising test execution speed
    * when the condition is quickly met.
    *
    * @example
    * async_test(t => {
    *  const popup = window.open("resources/coop-coep.py?coop=same-origin&coep=&navigate=about:blank");
    *  t.add_cleanup(() => popup.close());
    *  assert_equals(window, popup.opener);
    *
    *  popup.onload = t.step_func(() => {
    *    assert_true(popup.location.href.endsWith("&navigate=about:blank"));
    *    // Use step_wait_func_done as about:blank cannot message back.
    *    t.step_wait_func_done(() => popup.location.href === "about:blank");
    *  });
    * }, "Navigating a popup to about:blank");
    *
    * @param {Function} cond A function taking no arguments and
    *                        returning a boolean or a Promise. The callback is
    *                        called when this function returns true, or the
    *                        returned Promise is resolved with true.
    * @param {Function} func A function taking no arguments to call once
    *                        the condition is met.
    * @param {string} [description] Error message to add to assert in case of
    *                               failure.
    * @param {number} timeout Timeout in ms. This is multiplied by the global
    *                         timeout_multiplier
    * @param {number} interval Polling interval in ms
    *
    */
   Test.prototype.step_wait_func_done = function(cond, func, description,
                                                 timeout=3000, interval=100) {
        this.step_wait_func(cond, () => {
           if (func) {
               func();
           }
           this.done();
        }, description, timeout, interval);
   };

   /**
    * Poll for a function to return true, and resolve a promise
    * once it does, or assert if a timeout is reached. This is
    * preferred over a simple step_timeout whenever possible
    * since it allows the timeout to be longer to reduce
    * intermittents without compromising test execution speed
    * when the condition is quickly met.
    *
    * @example
    * promise_test(async t => {
    *  // …
    * await t.step_wait(() => frame.contentDocument === null, "Frame navigated to a cross-origin document");
    * // …
    * }, "");
    *
    * @param {Function} cond A function taking no arguments and
    *                        returning a boolean or a Promise.
    * @param {string} [description] Error message to add to assert in case of
    *                              failure.
    * @param {number} timeout Timeout in ms. This is multiplied by the global
    *                         timeout_multiplier
    * @param {number} interval Polling interval in ms
    * @returns {Promise} Promise resolved once cond is met.
    *
    */
   Test.prototype.step_wait = function(cond, description, timeout=3000, interval=100) {
       return new Promise(resolve => {
           this.step_wait_func(cond, resolve, description, timeout, interval);
       });
   };

   /*
    * Private method for registering cleanup functions. `testharness.js`
    * internals should use this method instead of the public `add_cleanup`
    * method in order to hide implementation details from the harness status
    * message in the case errors.
    */
   Test.prototype._add_cleanup = function(callback) {
       this.cleanup_callbacks.push(callback);
   };

   /**
    * Schedule a function to be run after the test result is known, regardless
    * of passing or failing state.
    *
    * The behavior of this function will not
    * influence the result of the test, but if an exception is thrown, the
    * test harness will report an error.
    *
    * @param {Function} callback - The cleanup function to run. This
    * is called with no arguments.
    */
   Test.prototype.add_cleanup = function(callback) {
       this._user_defined_cleanup_count += 1;
       this._add_cleanup(callback);
   };

   Test.prototype.set_timeout = function()
   {
       if (this.timeout_length !== null) {
           var this_obj = this;
           this.timeout_id = setTimeout(function()
                                        {
                                            this_obj.timeout();
                                        }, this.timeout_length);
       }
   };

   Test.prototype.set_status = function(status, message, stack)
   {
       this.status = status;
       this.message = message;
       this.stack = stack ? stack : null;
   };

   /**
    * Manually set the test status to ``TIMEOUT``.
    */
   Test.prototype.timeout = function()
   {
       this.timeout_id = null;
       this.set_status(this.TIMEOUT, "Test timed out");
       this.phase = this.phases.HAS_RESULT;
       this.done();
   };

   /**
    * Manually set the test status to ``TIMEOUT``.
    *
    * Alias for `Test.timeout <#Test.timeout>`_.
    */
   Test.prototype.force_timeout = function() {
       return this.timeout();
   };

   /**
    * Mark the test as complete.
    *
    * This sets the test status to ``PASS`` if no other status was
    * already recorded. Any subsequent attempts to run additional
    * test steps will be ignored.
    *
    * After setting the test status any test cleanup functions will
    * be run.
    */
   Test.prototype.done = function()
   {
       if (this.phase >= this.phases.CLEANING) {
           return;
       }

       if (this.phase <= this.phases.STARTED) {
           this.set_status(this.PASS, null);
       }

       if (global_scope.clearTimeout) {
           clearTimeout(this.timeout_id);
       }

       if (settings.debug) {
           console.log("TEST DONE",
                       this.status,
                       this.name);
       }

       this.cleanup();
   };

   function add_test_done_callback(test, callback)
   {
       if (test.phase === test.phases.COMPLETE) {
           callback();
           return;
       }

       test._done_callbacks.push(callback);
   }

   /*
    * Invoke all specified cleanup functions. If one or more produce an error,
    * the context is in an unpredictable state, so all further testing should
    * be cancelled.
    */
   Test.prototype.cleanup = function() {
       var errors = [];
       var bad_value_count = 0;
       function on_error(e) {
           errors.push(e);
           // Abort tests immediately so that tests declared within subsequent
           // cleanup functions are not run.
           tests.abort();
       }
       var this_obj = this;
       var results = [];

       this.phase = this.phases.CLEANING;

       if (this._abortController) {
           this._abortController.abort("Test cleanup");
       }

       forEach(this.cleanup_callbacks,
               function(cleanup_callback) {
                   var result;

                   try {
                       result = cleanup_callback();
                   } catch (e) {
                       on_error(e);
                       return;
                   }

                   if (!is_valid_cleanup_result(this_obj, result)) {
                       bad_value_count += 1;
                       // Abort tests immediately so that tests declared
                       // within subsequent cleanup functions are not run.
                       tests.abort();
                   }

                   results.push(result);
               });

       if (!this._is_promise_test) {
           cleanup_done(this_obj, errors, bad_value_count);
       } else {
           all_async(results,
                     function(result, done) {
                         if (result && typeof result.then === "function") {
                             result
                                 .then(null, on_error)
                                 .then(done);
                         } else {
                             done();
                         }
                     },
                     function() {
                         cleanup_done(this_obj, errors, bad_value_count);
                     });
       }
   };

   /*
    * Determine if the return value of a cleanup function is valid for a given
    * test. Any test may return the value `undefined`. Tests created with
    * `promise_test` may alternatively return "thenable" object values.
    */
   function is_valid_cleanup_result(test, result) {
       if (result === undefined) {
           return true;
       }

       if (test._is_promise_test) {
           return result && typeof result.then === "function";
       }

       return false;
   }

   function cleanup_done(test, errors, bad_value_count) {
       if (errors.length || bad_value_count) {
           var total = test._user_defined_cleanup_count;

           tests.status.status = tests.status.ERROR;
           tests.status.stack = null;
           tests.status.message = "Test named '" + test.name +
               "' specified " + total +
               " 'cleanup' function" + (total > 1 ? "s" : "");

           if (errors.length) {
               tests.status.message += ", and " + errors.length + " failed";
               tests.status.stack = ((typeof errors[0] === "object" &&
                                      errors[0].hasOwnProperty("stack")) ?
                                     errors[0].stack : null);
           }

           if (bad_value_count) {
               var type = test._is_promise_test ?
                  "non-thenable" : "non-undefined";
               tests.status.message += ", and " + bad_value_count +
                   " returned a " + type + " value";
           }

           tests.status.message += ".";
       }

       test.phase = test.phases.COMPLETE;
       tests.result(test);
       forEach(test._done_callbacks,
               function(callback) {
                   callback();
               });
       test._done_callbacks.length = 0;
   }

   /**
    * Gives an AbortSignal that will be aborted when the test finishes.
    */
   Test.prototype.get_signal = function() {
       if (!this._abortController) {
           throw new Error("AbortController is not supported in this browser");
       }
       return this._abortController.signal;
   };

   /**
    * A RemoteTest object mirrors a Test object on a remote worker. The
    * associated RemoteWorker updates the RemoteTest object in response to
    * received events. In turn, the RemoteTest object replicates these events
    * on the local document. This allows listeners (test result reporting
    * etc..) to transparently handle local and remote events.
    */
   function RemoteTest(clone) {
       var this_obj = this;
       Object.keys(clone).forEach(
               function(key) {
                   this_obj[key] = clone[key];
               });
       this.index = null;
       this.phase = this.phases.INITIAL;
       this.update_state_from(clone);
       this._done_callbacks = [];
       tests.push(this);
   }

   RemoteTest.prototype.structured_clone = function() {
       var clone = {};
       Object.keys(this).forEach(
               (function(key) {
                   var value = this[key];
                   // `RemoteTest` instances are responsible for managing
                   // their own "done" callback functions, so those functions
                   // are not relevant in other execution contexts. Because of
                   // this (and because Function values cannot be serialized
                   // for cross-realm transmittance), the property should not
                   // be considered when cloning instances.
                   if (key === '_done_callbacks' ) {
                       return;
                   }

                   if (typeof value === "object" && value !== null) {
                       clone[key] = merge({}, value);
                   } else {
                       clone[key] = value;
                   }
               }).bind(this));
       clone.phases = merge({}, this.phases);
       return clone;
   };

   /**
    * `RemoteTest` instances are objects which represent tests running in
    * another realm. They do not define "cleanup" functions (if necessary,
    * such functions are defined on the associated `Test` instance within the
    * external realm). However, `RemoteTests` may have "done" callbacks (e.g.
    * as attached by the `Tests` instance responsible for tracking the overall
    * test status in the parent realm). The `cleanup` method delegates to
    * `done` in order to ensure that such callbacks are invoked following the
    * completion of the `RemoteTest`.
    */
   RemoteTest.prototype.cleanup = function() {
       this.done();
   };
   RemoteTest.prototype.phases = Test.prototype.phases;
   RemoteTest.prototype.update_state_from = function(clone) {
       this.status = clone.status;
       this.message = clone.message;
       this.stack = clone.stack;
       if (this.phase === this.phases.INITIAL) {
           this.phase = this.phases.STARTED;
       }
   };
   RemoteTest.prototype.done = function() {
       this.phase = this.phases.COMPLETE;

       forEach(this._done_callbacks,
               function(callback) {
                   callback();
               });
   };

   RemoteTest.prototype.format_status = function() {
       return Test.prototype.status_formats[this.status];
   };

   /*
    * A RemoteContext listens for test events from a remote test context, such
    * as another window or a worker. These events are then used to construct
    * and maintain RemoteTest objects that mirror the tests running in the
    * remote context.
    *
    * An optional third parameter can be used as a predicate to filter incoming
    * MessageEvents.
    */
   function RemoteContext(remote, message_target, message_filter) {
       this.running = true;
       this.started = false;
       this.tests = new Array();
       this.early_exception = null;

       var this_obj = this;
       // If remote context is cross origin assigning to onerror is not
       // possible, so silently catch those errors.
       try {
         remote.onerror = function(error) { this_obj.remote_error(error); };
       } catch (e) {
         // Ignore.
       }

       // Keeping a reference to the remote object and the message handler until
       // remote_done() is seen prevents the remote object and its message channel
       // from going away before all the messages are dispatched.
       this.remote = remote;
       this.message_target = message_target;
       this.message_handler = function(message) {
           var passesFilter = !message_filter || message_filter(message);
           // The reference to the `running` property in the following
           // condition is unnecessary because that value is only set to
           // `false` after the `message_handler` function has been
           // unsubscribed.
           // TODO: Simplify the condition by removing the reference.
           if (this_obj.running && message.data && passesFilter &&
               (message.data.type in this_obj.message_handlers)) {
               this_obj.message_handlers[message.data.type].call(this_obj, message.data);
           }
       };

       if (self.Promise) {
           this.done = new Promise(function(resolve) {
               this_obj.doneResolve = resolve;
           });
       }

       this.message_target.addEventListener("message", this.message_handler);
   }

   RemoteContext.prototype.remote_error = function(error) {
       if (error.preventDefault) {
           error.preventDefault();
       }

       // Defer interpretation of errors until the testing protocol has
       // started and the remote test's `allow_uncaught_exception` property
       // is available.
       if (!this.started) {
           this.early_exception = error;
       } else if (!this.allow_uncaught_exception) {
           this.report_uncaught(error);
       }
   };

   RemoteContext.prototype.report_uncaught = function(error) {
       var message = error.message || String(error);
       var filename = (error.filename ? " " + error.filename: "");
       // FIXME: Display remote error states separately from main document
       // error state.
       tests.set_status(tests.status.ERROR,
                        "Error in remote" + filename + ": " + message,
                        error.stack);
   };

   RemoteContext.prototype.start = function(data) {
       this.started = true;
       this.allow_uncaught_exception = data.properties.allow_uncaught_exception;

       if (this.early_exception && !this.allow_uncaught_exception) {
           this.report_uncaught(this.early_exception);
       }
   };

   RemoteContext.prototype.test_state = function(data) {
       var remote_test = this.tests[data.test.index];
       if (!remote_test) {
           remote_test = new RemoteTest(data.test);
           this.tests[data.test.index] = remote_test;
       }
       remote_test.update_state_from(data.test);
       tests.notify_test_state(remote_test);
   };

   RemoteContext.prototype.test_done = function(data) {
       var remote_test = this.tests[data.test.index];
       remote_test.update_state_from(data.test);
       remote_test.done();
       tests.result(remote_test);
   };

   RemoteContext.prototype.remote_done = function(data) {
       if (tests.status.status === null &&
           data.status.status !== data.status.OK) {
           tests.set_status(data.status.status, data.status.message, data.status.stack);
       }

       for (let assert of data.asserts) {
           var record = new AssertRecord();
           record.assert_name = assert.assert_name;
           record.args = assert.args;
           record.test = assert.test != null ? this.tests[assert.test.index] : null;
           record.status = assert.status;
           record.stack = assert.stack;
           tests.asserts_run.push(record);
       }

       this.message_target.removeEventListener("message", this.message_handler);
       this.running = false;

       // If remote context is cross origin assigning to onerror is not
       // possible, so silently catch those errors.
       try {
         this.remote.onerror = null;
       } catch (e) {
         // Ignore.
       }

       this.remote = null;
       this.message_target = null;
       if (this.doneResolve) {
           this.doneResolve();
       }

       if (tests.all_done()) {
           tests.complete();
       }
   };

   RemoteContext.prototype.message_handlers = {
       start: RemoteContext.prototype.start,
       test_state: RemoteContext.prototype.test_state,
       result: RemoteContext.prototype.test_done,
       complete: RemoteContext.prototype.remote_done
   };

   /**
    * @class
    * Status of the overall harness
    */
   function TestsStatus()
   {
       /** The status code */
       this.status = null;
       /** Message in case of failure */
       this.message = null;
       /** Stack trace in case of an exception. */
       this.stack = null;
   }

   /**
    * Enum of possible harness statuses.
    *
    * :values:
    *   - ``OK``
    *   - ``ERROR``
    *   - ``TIMEOUT``
    *   - ``PRECONDITION_FAILED``
    */
   TestsStatus.statuses = {
       OK:0,
       ERROR:1,
       TIMEOUT:2,
       PRECONDITION_FAILED:3
   };

   TestsStatus.prototype = merge({}, TestsStatus.statuses);

   TestsStatus.prototype.formats = {
       0: "OK",
       1: "Error",
       2: "Timeout",
       3: "Optional Feature Unsupported"
   };

   TestsStatus.prototype.structured_clone = function()
   {
       if (!this._structured_clone) {
           var msg = this.message;
           msg = msg ? String(msg) : msg;
           this._structured_clone = merge({
               status:this.status,
               message:msg,
               stack:this.stack
           }, TestsStatus.statuses);
       }
       return this._structured_clone;
   };

   TestsStatus.prototype.format_status = function() {
       return this.formats[this.status];
   };

   /**
    * @class
    * Record of an assert that ran.
    *
    * @param {Test} test - The test which ran the assert.
    * @param {string} assert_name - The function name of the assert.
    * @param {Any} args - The arguments passed to the assert function.
    */
   function AssertRecord(test, assert_name, args = []) {
       /** Name of the assert that ran */
       this.assert_name = assert_name;
       /** Test that ran the assert */
       this.test = test;
       // Avoid keeping complex objects alive
       /** Stringification of the arguments that were passed to the assert function */
       this.args = args.map(x => format_value(x).replace(/\n/g, " "));
       /** Status of the assert */
       this.status = null;
   }

   AssertRecord.prototype.structured_clone = function() {
       return {
           assert_name: this.assert_name,
           test: this.test ? this.test.structured_clone() : null,
           args: this.args,
           status: this.status,
       };
   };

   function Tests()
   {
       this.tests = [];
       this.num_pending = 0;

       this.phases = {
           INITIAL:0,
           SETUP:1,
           HAVE_TESTS:2,
           HAVE_RESULTS:3,
           COMPLETE:4
       };
       this.phase = this.phases.INITIAL;

       this.properties = {};

       this.wait_for_finish = false;
       this.processing_callbacks = false;

       this.allow_uncaught_exception = false;

       this.file_is_test = false;
       // This value is lazily initialized in order to avoid introducing a
       // dependency on ECMAScript 2015 Promises to all tests.
       this.promise_tests = null;
       this.promise_setup_called = false;

       this.timeout_multiplier = 1;
       this.timeout_length = test_environment.test_timeout();
       this.timeout_id = null;

       this.start_callbacks = [];
       this.test_state_callbacks = [];
       this.test_done_callbacks = [];
       this.all_done_callbacks = [];

       this.hide_test_state = false;
       this.remotes = [];

       this.current_test = null;
       this.asserts_run = [];

       // Track whether output is enabled, and thus whether or not we should
       // track asserts.
       //
       // On workers we don't get properties set from testharnessreport.js, so
       // we don't know whether or not to track asserts. To avoid the
       // resulting performance hit, we assume we are not meant to. This means
       // that assert tracking does not function on workers.
       this.output = settings.output && 'document' in global_scope;

       this.status = new TestsStatus();

       var this_obj = this;

       test_environment.add_on_loaded_callback(function() {
           if (this_obj.all_done()) {
               this_obj.complete();
           }
       });

       this.set_timeout();
   }

   Tests.prototype.setup = function(func, properties)
   {
       if (this.phase >= this.phases.HAVE_RESULTS) {
           return;
       }

       if (this.phase < this.phases.SETUP) {
           this.phase = this.phases.SETUP;
       }

       this.properties = properties;

       for (var p in properties) {
           if (properties.hasOwnProperty(p)) {
               var value = properties[p];
               if (p === "allow_uncaught_exception") {
                   this.allow_uncaught_exception = value;
               } else if (p === "explicit_done" && value) {
                   this.wait_for_finish = true;
               } else if (p === "explicit_timeout" && value) {
                   this.timeout_length = null;
                   if (this.timeout_id)
                   {
                       clearTimeout(this.timeout_id);
                   }
               } else if (p === "single_test" && value) {
                   this.set_file_is_test();
               } else if (p === "timeout_multiplier") {
                   this.timeout_multiplier = value;
                   if (this.timeout_length) {
                        this.timeout_length *= this.timeout_multiplier;
                   }
               } else if (p === "hide_test_state") {
                   this.hide_test_state = value;
               } else if (p === "output") {
                   this.output = value;
               } else if (p === "debug") {
                   settings.debug = value;
               }
           }
       }

       if (func) {
           try {
               func();
           } catch (e) {
               this.status.status = e instanceof OptionalFeatureUnsupportedError ? this.status.PRECONDITION_FAILED : this.status.ERROR;
               this.status.message = String(e);
               this.status.stack = e.stack ? e.stack : null;
               this.complete();
           }
       }
       this.set_timeout();
   };

   Tests.prototype.set_file_is_test = function() {
       if (this.tests.length > 0) {
           throw new Error("Tried to set file as test after creating a test");
       }
       this.wait_for_finish = true;
       this.file_is_test = true;
       // Create the test, which will add it to the list of tests
       tests.current_test = async_test();
   };

   Tests.prototype.set_status = function(status, message, stack)
   {
       this.status.status = status;
       this.status.message = message;
       this.status.stack = stack ? stack : null;
   };

   Tests.prototype.set_timeout = function() {
       if (global_scope.clearTimeout) {
           var this_obj = this;
           clearTimeout(this.timeout_id);
           if (this.timeout_length !== null) {
               this.timeout_id = setTimeout(function() {
                                                this_obj.timeout();
                                            }, this.timeout_length);
           }
       }
   };

   Tests.prototype.timeout = function() {
       var test_in_cleanup = null;

       if (this.status.status === null) {
           forEach(this.tests,
                   function(test) {
                       // No more than one test is expected to be in the
                       // "CLEANUP" phase at any time
                       if (test.phase === test.phases.CLEANING) {
                           test_in_cleanup = test;
                       }

                       test.phase = test.phases.COMPLETE;
                   });

           // Timeouts that occur while a test is in the "cleanup" phase
           // indicate that some global state was not properly reverted. This
           // invalidates the overall test execution, so the timeout should be
           // reported as an error and cancel the execution of any remaining
           // tests.
           if (test_in_cleanup) {
               this.status.status = this.status.ERROR;
               this.status.message = "Timeout while running cleanup for " +
                   "test named \"" + test_in_cleanup.name + "\".";
               tests.status.stack = null;
           } else {
               this.status.status = this.status.TIMEOUT;
           }
       }

       this.complete();
   };

   Tests.prototype.end_wait = function()
   {
       this.wait_for_finish = false;
       if (this.all_done()) {
           this.complete();
       }
   };

   Tests.prototype.push = function(test)
   {
       if (this.phase === this.phases.COMPLETE) {
           return;
       }
       if (this.phase < this.phases.HAVE_TESTS) {
           this.start();
       }
       this.num_pending++;
       test.index = this.tests.push(test) - 1;
       this.notify_test_state(test);
   };

   Tests.prototype.notify_test_state = function(test) {
       var this_obj = this;
       forEach(this.test_state_callbacks,
               function(callback) {
                   callback(test, this_obj);
               });
   };

   Tests.prototype.all_done = function() {
       return (this.tests.length > 0 || this.remotes.length > 0) &&
               test_environment.all_loaded &&
               (this.num_pending === 0 || this.is_aborted) && !this.wait_for_finish &&
               !this.processing_callbacks &&
               !this.remotes.some(function(w) { return w.running; });
   };

   Tests.prototype.start = function() {
       this.phase = this.phases.HAVE_TESTS;
       this.notify_start();
   };

   Tests.prototype.notify_start = function() {
       var this_obj = this;
       forEach (this.start_callbacks,
                function(callback)
                {
                    callback(this_obj.properties);
                });
   };

   Tests.prototype.result = function(test)
   {
       // If the harness has already transitioned beyond the `HAVE_RESULTS`
       // phase, subsequent tests should not cause it to revert.
       if (this.phase <= this.phases.HAVE_RESULTS) {
           this.phase = this.phases.HAVE_RESULTS;
       }
       this.num_pending--;
       this.notify_result(test);
   };

   Tests.prototype.notify_result = function(test) {
       var this_obj = this;
       this.processing_callbacks = true;
       forEach(this.test_done_callbacks,
               function(callback)
               {
                   callback(test, this_obj);
               });
       this.processing_callbacks = false;
       if (this_obj.all_done()) {
           this_obj.complete();
       }
   };

   Tests.prototype.complete = function() {
       if (this.phase === this.phases.COMPLETE) {
           return;
       }
       var this_obj = this;
       var all_complete = function() {
           this_obj.phase = this_obj.phases.COMPLETE;
           this_obj.notify_complete();
       };
       var incomplete = filter(this.tests,
                               function(test) {
                                   return test.phase < test.phases.COMPLETE;
                               });

       /**
        * To preserve legacy behavior, overall test completion must be
        * signaled synchronously.
        */
       if (incomplete.length === 0) {
           all_complete();
           return;
       }

       all_async(incomplete,
                 function(test, testDone)
                 {
                     if (test.phase === test.phases.INITIAL) {
                         test.phase = test.phases.HAS_RESULT;
                         test.done();
                         testDone();
                     } else {
                         add_test_done_callback(test, testDone);
                         test.cleanup();
                     }
                 },
                 all_complete);
   };

   Tests.prototype.set_assert = function(assert_name, args) {
       this.asserts_run.push(new AssertRecord(this.current_test, assert_name, args));
   };

   Tests.prototype.set_assert_status = function(index, status, stack) {
       let assert_record = this.asserts_run[index];
       assert_record.status = status;
       assert_record.stack = stack;
   };

   /**
    * Update the harness status to reflect an unrecoverable harness error that
    * should cancel all further testing. Update all previously-defined tests
    * which have not yet started to indicate that they will not be executed.
    */
   Tests.prototype.abort = function() {
       this.status.status = this.status.ERROR;
       this.is_aborted = true;

       forEach(this.tests,
               function(test) {
                   if (test.phase === test.phases.INITIAL) {
                       test.phase = test.phases.COMPLETE;
                   }
               });
   };

   /*
    * Determine if any tests share the same `name` property. Return an array
    * containing the names of any such duplicates.
    */
   Tests.prototype.find_duplicates = function() {
       var names = Object.create(null);
       var duplicates = [];

       forEach (this.tests,
                function(test)
                {
                    if (test.name in names && duplicates.indexOf(test.name) === -1) {
                       duplicates.push(test.name);
                    }
                    names[test.name] = true;
                });

       return duplicates;
   };

   function code_unit_str(char) {
       return 'U+' + char.charCodeAt(0).toString(16);
   }

   function sanitize_unpaired_surrogates(str) {
       return str.replace(
           /([\ud800-\udbff]+)(?![\udc00-\udfff])|(^|[^\ud800-\udbff])([\udc00-\udfff]+)/g,
           function(_, low, prefix, high) {
               var output = prefix || "";  // prefix may be undefined
               var string = low || high;  // only one of these alternates can match
               for (var i = 0; i < string.length; i++) {
                   output += code_unit_str(string[i]);
               }
               return output;
           });
   }

   function sanitize_all_unpaired_surrogates(tests) {
       forEach (tests,
                function (test)
                {
                    var sanitized = sanitize_unpaired_surrogates(test.name);

                    if (test.name !== sanitized) {
                        test.name = sanitized;
                        delete test._structured_clone;
                    }
                });
   }

   Tests.prototype.notify_complete = function() {
       var this_obj = this;
       var duplicates;

       if (this.status.status === null) {
           duplicates = this.find_duplicates();

           // Some transports adhere to UTF-8's restriction on unpaired
           // surrogates. Sanitize the titles so that the results can be
           // consistently sent via all transports.
           sanitize_all_unpaired_surrogates(this.tests);

           // Test names are presumed to be unique within test files--this
           // allows consumers to use them for identification purposes.
           // Duplicated names violate this expectation and should therefore
           // be reported as an error.
           if (duplicates.length) {
               this.status.status = this.status.ERROR;
               this.status.message =
                  duplicates.length + ' duplicate test name' +
                  (duplicates.length > 1 ? 's' : '') + ': "' +
                  duplicates.join('", "') + '"';
           } else {
               this.status.status = this.status.OK;
           }
       }

       forEach (this.all_done_callbacks,
                function(callback)
                {
                    callback(this_obj.tests, this_obj.status, this_obj.asserts_run);
                });
   };

   /*
    * Constructs a RemoteContext that tracks tests from a specific worker.
    */
   Tests.prototype.create_remote_worker = function(worker) {
       var message_port;

       if (is_service_worker(worker)) {
           message_port = navigator.serviceWorker;
           worker.postMessage({type: "connect"});
       } else if (is_shared_worker(worker)) {
           message_port = worker.port;
           message_port.start();
       } else {
           message_port = worker;
       }

       return new RemoteContext(worker, message_port);
   };

   /*
    * Constructs a RemoteContext that tracks tests from a specific window.
    */
   Tests.prototype.create_remote_window = function(remote) {
       remote.postMessage({type: "getmessages"}, "*");
       return new RemoteContext(
           remote,
           window,
           function(msg) {
               return msg.source === remote;
           }
       );
   };

   Tests.prototype.fetch_tests_from_worker = function(worker) {
       if (this.phase >= this.phases.COMPLETE) {
           return;
       }

       var remoteContext = this.create_remote_worker(worker);
       this.remotes.push(remoteContext);
       return remoteContext.done;
   };

   /**
    * Get test results from a worker and include them in the current test.
    *
    * @param {Worker|SharedWorker|ServiceWorker|MessagePort} port -
    * Either a worker object or a port connected to a worker which is
    * running tests..
    * @returns {Promise} - A promise that's resolved once all the remote tests are complete.
    */
   function fetch_tests_from_worker(port) {
       return tests.fetch_tests_from_worker(port);
   }
   expose(fetch_tests_from_worker, 'fetch_tests_from_worker');

   Tests.prototype.fetch_tests_from_window = function(remote) {
       if (this.phase >= this.phases.COMPLETE) {
           return;
       }

       var remoteContext = this.create_remote_window(remote);
       this.remotes.push(remoteContext);
       return remoteContext.done;
   };

   /**
    * Aggregate tests from separate windows or iframes
    * into the current document as if they were all part of the same test file.
    *
    * The document of the second window (or iframe) should include
    * ``testharness.js``, but not ``testharnessreport.js``, and use
    * :js:func:`test`, :js:func:`async_test`, and :js:func:`promise_test` in
    * the usual manner.
    *
    * @param {Window} window - The window to fetch tests from.
    */
   function fetch_tests_from_window(window) {
       return tests.fetch_tests_from_window(window);
   }
   expose(fetch_tests_from_window, 'fetch_tests_from_window');

   /**
    * Get test results from a shadow realm and include them in the current test.
    *
    * @param {ShadowRealm} realm - A shadow realm also running the test harness
    * @returns {Promise} - A promise that's resolved once all the remote tests are complete.
    */
   function fetch_tests_from_shadow_realm(realm) {
       var chan = new MessageChannel();
       function receiveMessage(msg_json) {
           chan.port1.postMessage(JSON.parse(msg_json));
       }
       var done = tests.fetch_tests_from_worker(chan.port2);
       realm.evaluate("begin_shadow_realm_tests")(receiveMessage);
       chan.port2.start();
       return done;
   }
   expose(fetch_tests_from_shadow_realm, 'fetch_tests_from_shadow_realm');

   /**
    * Begin running tests in this shadow realm test harness.
    *
    * To be called after all tests have been loaded; it is an error to call
    * this more than once or in a non-Shadow Realm environment
    *
    * @param {Function} postMessage - A function to send test updates to the
    * incubating realm-- accepts JSON-encoded messages in the format used by
    * RemoteContext
    */
   function begin_shadow_realm_tests(postMessage) {
       if (!(test_environment instanceof ShadowRealmTestEnvironment)) {
           throw new Error("begin_shadow_realm_tests called in non-Shadow Realm environment");
       }

       test_environment.begin(function (msg) {
           postMessage(JSON.stringify(msg));
       });
   }
   expose(begin_shadow_realm_tests, 'begin_shadow_realm_tests');

   /**
    * Timeout the tests.
    *
    * This only has an effect when ``explicit_timeout`` has been set
    * in :js:func:`setup`. In other cases any call is a no-op.
    *
    */
   function timeout() {
       if (tests.timeout_length === null) {
           tests.timeout();
       }
   }
   expose(timeout, 'timeout');

   /**
    * Add a callback that's triggered when the first :js:class:`Test` is created.
    *
    * @param {Function} callback - Callback function. This is called
    * without arguments.
    */
   function add_start_callback(callback) {
       tests.start_callbacks.push(callback);
   }

   /**
    * Add a callback that's triggered when a test state changes.
    *
    * @param {Function} callback - Callback function, called with the
    * :js:class:`Test` as the only argument.
    */
   function add_test_state_callback(callback) {
       tests.test_state_callbacks.push(callback);
   }

   /**
    * Add a callback that's triggered when a test result is received.
    *
    * @param {Function} callback - Callback function, called with the
    * :js:class:`Test` as the only argument.
    */
   function add_result_callback(callback) {
       tests.test_done_callbacks.push(callback);
   }

   /**
    * Add a callback that's triggered when all tests are complete.
    *
    * @param {Function} callback - Callback function, called with an
    * array of :js:class:`Test` objects, a :js:class:`TestsStatus`
    * object and an array of :js:class:`AssertRecord` objects. If the
    * debug setting is ``false`` the final argument will be an empty
    * array.
    *
    * For performance reasons asserts are only tracked when the debug
    * setting is ``true``. In other cases the array of asserts will be
    * empty.
    */
   function add_completion_callback(callback) {
       tests.all_done_callbacks.push(callback);
   }

   expose(add_start_callback, 'add_start_callback');
   expose(add_test_state_callback, 'add_test_state_callback');
   expose(add_result_callback, 'add_result_callback');
   expose(add_completion_callback, 'add_completion_callback');

   function remove(array, item) {
       var index = array.indexOf(item);
       if (index > -1) {
           array.splice(index, 1);
       }
   }

   function remove_start_callback(callback) {
       remove(tests.start_callbacks, callback);
   }

   function remove_test_state_callback(callback) {
       remove(tests.test_state_callbacks, callback);
   }

   function remove_result_callback(callback) {
       remove(tests.test_done_callbacks, callback);
   }

   function remove_completion_callback(callback) {
      remove(tests.all_done_callbacks, callback);
   }

   /*
    * Output listener
   */

   function Output() {
       this.output_document = document;
       this.output_node = null;
       this.enabled = settings.output;
       this.phase = this.INITIAL;
   }

   Output.prototype.INITIAL = 0;
   Output.prototype.STARTED = 1;
   Output.prototype.HAVE_RESULTS = 2;
   Output.prototype.COMPLETE = 3;

   Output.prototype.setup = function(properties) {
       if (this.phase > this.INITIAL) {
           return;
       }

       //If output is disabled in testharnessreport.js the test shouldn't be
       //able to override that
       this.enabled = this.enabled && (properties.hasOwnProperty("output") ?
                                       properties.output : settings.output);
   };

   Output.prototype.init = function(properties) {
       if (this.phase >= this.STARTED) {
           return;
       }
       if (properties.output_document) {
           this.output_document = properties.output_document;
       } else {
           this.output_document = document;
       }
       this.phase = this.STARTED;
   };

   Output.prototype.resolve_log = function() {
       var output_document;
       if (this.output_node) {
           return;
       }
       if (typeof this.output_document === "function") {
           output_document = this.output_document.apply(undefined);
       } else {
           output_document = this.output_document;
       }
       if (!output_document) {
           return;
       }
       var node = output_document.getElementById("log");
       if (!node) {
           if (output_document.readyState === "loading") {
               return;
           }
           node = output_document.createElementNS("http://www.w3.org/1999/xhtml", "div");
           node.id = "log";
           if (output_document.body) {
               output_document.body.appendChild(node);
           } else {
               var root = output_document.documentElement;
               var is_html = (root &&
                              root.namespaceURI === "http://www.w3.org/1999/xhtml" &&
                              root.localName === "html");
               var is_svg = (output_document.defaultView &&
                             "SVGSVGElement" in output_document.defaultView &&
                             root instanceof output_document.defaultView.SVGSVGElement);
               if (is_svg) {
                   var foreignObject = output_document.createElementNS("http://www.w3.org/2000/svg", "foreignObject");
                   foreignObject.setAttribute("width", "100%");
                   foreignObject.setAttribute("height", "100%");
                   root.appendChild(foreignObject);
                   foreignObject.appendChild(node);
               } else if (is_html) {
                   root.appendChild(output_document.createElementNS("http://www.w3.org/1999/xhtml", "body"))
                       .appendChild(node);
               } else {
                   root.appendChild(node);
               }
           }
       }
       this.output_document = output_document;
       this.output_node = node;
   };

   Output.prototype.show_status = function() {
       if (this.phase < this.STARTED) {
           this.init({});
       }
       if (!this.enabled || this.phase === this.COMPLETE) {
           return;
       }
       this.resolve_log();
       if (this.phase < this.HAVE_RESULTS) {
           this.phase = this.HAVE_RESULTS;
       }
       var done_count = tests.tests.length - tests.num_pending;
       if (this.output_node && !tests.hide_test_state) {
           if (done_count < 100 ||
               (done_count < 1000 && done_count % 100 === 0) ||
               done_count % 1000 === 0) {
               this.output_node.textContent = "Running, " +
                   done_count + " complete, " +
                   tests.num_pending + " remain";
           }
       }
   };

   Output.prototype.show_results = function (tests, harness_status, asserts_run) {
       if (this.phase >= this.COMPLETE) {
           return;
       }
       if (!this.enabled) {
           return;
       }
       if (!this.output_node) {
           this.resolve_log();
       }
       this.phase = this.COMPLETE;

       var log = this.output_node;
       if (!log) {
           return;
       }
       var output_document = this.output_document;

       while (log.lastChild) {
           log.removeChild(log.lastChild);
       }

       var stylesheet = output_document.createElementNS(xhtml_ns, "style");
       stylesheet.textContent = stylesheetContent;
       var heads = output_document.getElementsByTagName("head");
       if (heads.length) {
           heads[0].appendChild(stylesheet);
       }

       var status_number = {};
       forEach(tests,
               function(test) {
                   var status = test.format_status();
                   if (status_number.hasOwnProperty(status)) {
                       status_number[status] += 1;
                   } else {
                       status_number[status] = 1;
                   }
               });

       function status_class(status)
       {
           return status.replace(/\s/g, '').toLowerCase();
       }

       var summary_template = ["section", {"id":"summary"},
                               ["h2", {}, "Summary"],
                               function()
                               {
                                   var status = harness_status.format_status();
                                   var rv = [["section", {},
                                              ["p", {},
                                               "Harness status: ",
                                               ["span", {"class":status_class(status)},
                                                status
                                               ],
                                              ],
                                              ["button", {"id":"rerun"}, "Rerun"]
                                             ]];

                                   if (harness_status.status === harness_status.ERROR) {
                                       rv[0].push(["pre", {}, harness_status.message]);
                                       if (harness_status.stack) {
                                           rv[0].push(["pre", {}, harness_status.stack]);
                                       }
                                   }
                                   return rv;
                               },
                               ["p", {}, "Found ${num_tests} tests"],
                               function() {
                                   var rv = [["div", {}]];
                                   var i = 0;
                                   while (Test.prototype.status_formats.hasOwnProperty(i)) {
                                       if (status_number.hasOwnProperty(Test.prototype.status_formats[i])) {
                                           var status = Test.prototype.status_formats[i];
                                           rv[0].push(["div", {},
                                                       ["label", {},
                                                        ["input", {type:"checkbox", checked:"checked"}],
                                                        status_number[status] + " ",
                                                        ["span", {"class":status_class(status)}, status]]]);
                                       }
                                       i++;
                                   }
                                   return rv;
                               },
                              ];

       log.appendChild(render(summary_template, {num_tests:tests.length}, output_document));

       output_document.getElementById("rerun").addEventListener("click",
           function() {
               let evt = new Event('__test_restart');
               let canceled = !window.dispatchEvent(evt);
               if (!canceled) { location.reload(); }
           });

       forEach(output_document.querySelectorAll("section#summary label"),
               function(element)
               {
                   on_event(element, "click",
                            function(e)
                            {
                                if (output_document.getElementById("results") === null) {
                                    e.preventDefault();
                                    return;
                                }
                                var result_class = element.querySelector("span[class]").getAttribute("class");
                                var style_element = output_document.querySelector("style#hide-" + result_class);
                                var input_element = element.querySelector("input");
                                if (!style_element && !input_element.checked) {
                                    style_element = output_document.createElementNS(xhtml_ns, "style");
                                    style_element.id = "hide-" + result_class;
                                    style_element.textContent = "table#results > tbody > tr.overall-"+result_class+"{display:none}";
                                    output_document.body.appendChild(style_element);
                                } else if (style_element && input_element.checked) {
                                    style_element.parentNode.removeChild(style_element);
                                }
                            });
               });

       function has_assertions()
       {
           for (var i = 0; i < tests.length; i++) {
               if (tests[i].properties.hasOwnProperty("assert")) {
                   return true;
               }
           }
           return false;
       }

       function get_assertion(test)
       {
           if (test.properties.hasOwnProperty("assert")) {
               if (Array.isArray(test.properties.assert)) {
                   return test.properties.assert.join(' ');
               }
               return test.properties.assert;
           }
           return '';
       }

       var asserts_run_by_test = new Map();
       asserts_run.forEach(assert => {
           if (!asserts_run_by_test.has(assert.test)) {
               asserts_run_by_test.set(assert.test, []);
           }
           asserts_run_by_test.get(assert.test).push(assert);
       });

       function get_asserts_output(test) {
           const asserts_output = render(
               ["details", {},
                   ["summary", {}, "Asserts run"],
                   ["table", {}, ""] ]);

           var asserts = asserts_run_by_test.get(test);
           if (!asserts) {
               asserts_output.querySelector("summary").insertAdjacentText("afterend", "No asserts ran");
               return asserts_output;
           }

           const table = asserts_output.querySelector("table");
           for (const assert of asserts) {
               const status_class_name = status_class(Test.prototype.status_formats[assert.status]);
               var output_fn = "(" + assert.args.join(", ") + ")";
               if (assert.stack) {
                   output_fn += "\n";
                   output_fn += assert.stack.split("\n", 1)[0].replace(/@?\w+:\/\/[^ "\/]+(?::\d+)?/g, " ");
               }
               table.appendChild(render(
                   ["tr", {"class":"overall-" + status_class_name},
                       ["td", {"class":status_class_name}, Test.prototype.status_formats[assert.status]],
                       ["td", {}, ["pre", {}, ["strong", {}, assert.assert_name], output_fn]] ]));
           }
           return asserts_output;
       }

       var assertions = has_assertions();
       const section = render(
           ["section", {},
               ["h2", {}, "Details"],
               ["table", {"id":"results", "class":(assertions ? "assertions" : "")},
                   ["thead", {},
                       ["tr", {},
                           ["th", {}, "Result"],
                           ["th", {}, "Test Name"],
                           (assertions ? ["th", {}, "Assertion"] : ""),
                           ["th", {}, "Message" ]]],
                   ["tbody", {}]]]);

       const tbody = section.querySelector("tbody");
       for (const test of tests) {
           const status = test.format_status();
           const status_class_name = status_class(status);
           tbody.appendChild(render(
               ["tr", {"class":"overall-" + status_class_name},
                   ["td", {"class":status_class_name}, status],
                   ["td", {}, test.name],
                   (assertions ? ["td", {}, get_assertion(test)] : ""),
                   ["td", {},
                       test.message ?? "",
                       ["pre", {}, test.stack ?? ""]]]));
           if (!(test instanceof RemoteTest)) {
               tbody.lastChild.lastChild.appendChild(get_asserts_output(test));
           }
       }
       log.appendChild(section);
   };

   /*
    * Template code
    *
    * A template is just a JavaScript structure. An element is represented as:
    *
    * [tag_name, {attr_name:attr_value}, child1, child2]
    *
    * the children can either be strings (which act like text nodes), other templates or
    * functions (see below)
    *
    * A text node is represented as
    *
    * ["{text}", value]
    *
    * String values have a simple substitution syntax; ${foo} represents a variable foo.
    *
    * It is possible to embed logic in templates by using a function in a place where a
    * node would usually go. The function must either return part of a template or null.
    *
    * In cases where a set of nodes are required as output rather than a single node
    * with children it is possible to just use a list
    * [node1, node2, node3]
    *
    * Usage:
    *
    * render(template, substitutions) - take a template and an object mapping
    * variable names to parameters and return either a DOM node or a list of DOM nodes
    *
    * substitute(template, substitutions) - take a template and variable mapping object,
    * make the variable substitutions and return the substituted template
    *
    */

   function is_single_node(template)
   {
       return typeof template[0] === "string";
   }

   function substitute(template, substitutions)
   {
       if (typeof template === "function") {
           var replacement = template(substitutions);
           if (!replacement) {
               return null;
           }

           return substitute(replacement, substitutions);
       }

       if (is_single_node(template)) {
           return substitute_single(template, substitutions);
       }

       return filter(map(template, function(x) {
                             return substitute(x, substitutions);
                         }), function(x) {return x !== null;});
   }

   function substitute_single(template, substitutions)
   {
       var substitution_re = /\$\{([^ }]*)\}/g;

       function do_substitution(input)
       {
           var components = input.split(substitution_re);
           var rv = [];
           if (components.length === 1) {
               rv = components;
           } else if (substitutions) {
               for (var i = 0; i < components.length; i += 2) {
                   if (components[i]) {
                       rv.push(components[i]);
                   }
                   if (substitutions[components[i + 1]]) {
                       rv.push(String(substitutions[components[i + 1]]));
                   }
               }
           }
           return rv;
       }

       function substitute_attrs(attrs, rv)
       {
           rv[1] = {};
           for (var name in template[1]) {
               if (attrs.hasOwnProperty(name)) {
                   var new_name = do_substitution(name).join("");
                   var new_value = do_substitution(attrs[name]).join("");
                   rv[1][new_name] = new_value;
               }
           }
       }

       function substitute_children(children, rv)
       {
           for (var i = 0; i < children.length; i++) {
               if (children[i] instanceof Object) {
                   var replacement = substitute(children[i], substitutions);
                   if (replacement !== null) {
                       if (is_single_node(replacement)) {
                           rv.push(replacement);
                       } else {
                           extend(rv, replacement);
                       }
                   }
               } else {
                   extend(rv, do_substitution(String(children[i])));
               }
           }
           return rv;
       }

       var rv = [];
       rv.push(do_substitution(String(template[0])).join(""));

       if (template[0] === "{text}") {
           substitute_children(template.slice(1), rv);
       } else {
           substitute_attrs(template[1], rv);
           substitute_children(template.slice(2), rv);
       }

       return rv;
   }

   function make_dom_single(template, doc)
   {
       var output_document = doc || document;
       var element;
       if (template[0] === "{text}") {
           element = output_document.createTextNode("");
           for (var i = 1; i < template.length; i++) {
               element.data += template[i];
           }
       } else {
           element = output_document.createElementNS(xhtml_ns, template[0]);
           for (var name in template[1]) {
               if (template[1].hasOwnProperty(name)) {
                   element.setAttribute(name, template[1][name]);
               }
           }
           for (var i = 2; i < template.length; i++) {
               if (template[i] instanceof Object) {
                   var sub_element = make_dom(template[i]);
                   element.appendChild(sub_element);
               } else {
                   var text_node = output_document.createTextNode(template[i]);
                   element.appendChild(text_node);
               }
           }
       }

       return element;
   }

   function make_dom(template, substitutions, output_document)
   {
       if (is_single_node(template)) {
           return make_dom_single(template, output_document);
       }

       return map(template, function(x) {
                      return make_dom_single(x, output_document);
                  });
   }

   function render(template, substitutions, output_document)
   {
       return make_dom(substitute(template, substitutions), output_document);
   }

   /*
    * Utility functions
    */
   function assert(expected_true, function_name, description, error, substitutions)
   {
       if (expected_true !== true) {
           var msg = make_message(function_name, description,
                                  error, substitutions);
           throw new AssertionError(msg);
       }
   }

   /**
    * @class
    * Exception type that represents a failing assert.
    *
    * @param {string} message - Error message.
    */
   function AssertionError(message)
   {
       if (typeof message === "string") {
           message = sanitize_unpaired_surrogates(message);
       }
       this.message = message;
       this.stack = get_stack();
   }
   expose(AssertionError, "AssertionError");

   AssertionError.prototype = Object.create(Error.prototype);

   const get_stack = function() {
       var stack = new Error().stack;

       // 'Error.stack' is not supported in all browsers/versions
       if (!stack) {
           return "(Stack trace unavailable)";
       }

       var lines = stack.split("\n");

       // Create a pattern to match stack frames originating within testharness.js.  These include the
       // script URL, followed by the line/col (e.g., '/resources/testharness.js:120:21').
       // Escape the URL per http://stackoverflow.com/questions/3561493/is-there-a-regexp-escape-function-in-javascript
       // in case it contains RegExp characters.
       var script_url = get_script_url();
       var re_text = script_url ? script_url.replace(/[-\/\\^$*+?.()|[\]{}]/g, '\\$&') : "\\btestharness.js";
       var re = new RegExp(re_text + ":\\d+:\\d+");

       // Some browsers include a preamble that specifies the type of the error object.  Skip this by
       // advancing until we find the first stack frame originating from testharness.js.
       var i = 0;
       while (!re.test(lines[i]) && i < lines.length) {
           i++;
       }

       // Then skip the top frames originating from testharness.js to begin the stack at the test code.
       while (re.test(lines[i]) && i < lines.length) {
           i++;
       }

       // Paranoid check that we didn't skip all frames.  If so, return the original stack unmodified.
       if (i >= lines.length) {
           return stack;
       }

       return lines.slice(i).join("\n");
   };

   function OptionalFeatureUnsupportedError(message)
   {
       AssertionError.call(this, message);
   }
   OptionalFeatureUnsupportedError.prototype = Object.create(AssertionError.prototype);
   expose(OptionalFeatureUnsupportedError, "OptionalFeatureUnsupportedError");

   function make_message(function_name, description, error, substitutions)
   {
       for (var p in substitutions) {
           if (substitutions.hasOwnProperty(p)) {
               substitutions[p] = format_value(substitutions[p]);
           }
       }
       var node_form = substitute(["{text}", "${function_name}: ${description}" + error],
                                  merge({function_name:function_name,
                                         description:(description?description + " ":"")},
                                         substitutions));
       return node_form.slice(1).join("");
   }

   function filter(array, callable, thisObj) {
       var rv = [];
       for (var i = 0; i < array.length; i++) {
           if (array.hasOwnProperty(i)) {
               var pass = callable.call(thisObj, array[i], i, array);
               if (pass) {
                   rv.push(array[i]);
               }
           }
       }
       return rv;
   }

   function map(array, callable, thisObj)
   {
       var rv = [];
       rv.length = array.length;
       for (var i = 0; i < array.length; i++) {
           if (array.hasOwnProperty(i)) {
               rv[i] = callable.call(thisObj, array[i], i, array);
           }
       }
       return rv;
   }

   function extend(array, items)
   {
       Array.prototype.push.apply(array, items);
   }

   function forEach(array, callback, thisObj)
   {
       for (var i = 0; i < array.length; i++) {
           if (array.hasOwnProperty(i)) {
               callback.call(thisObj, array[i], i, array);
           }
       }
   }

   /**
    * Immediately invoke a "iteratee" function with a series of values in
    * parallel and invoke a final "done" function when all of the "iteratee"
    * invocations have signaled completion.
    *
    * If all callbacks complete synchronously (or if no callbacks are
    * specified), the ``done_callback`` will be invoked synchronously. It is the
    * responsibility of the caller to ensure asynchronicity in cases where
    * that is desired.
    *
    * @param {array} value Zero or more values to use in the invocation of
    *                      ``iter_callback``
    * @param {function} iter_callback A function that will be invoked
    *                                 once for each of the values min
    *                                 ``value``. Two arguments will
    *                                 be available in each
    *                                 invocation: the value from
    *                                 ``value`` and a function that
    *                                 must be invoked to signal
    *                                 completion
    * @param {function} done_callback A function that will be invoked after
    *                                 all operations initiated by the
    *                                 ``iter_callback`` function have signaled
    *                                 completion
    */
   function all_async(values, iter_callback, done_callback)
   {
       var remaining = values.length;

       if (remaining === 0) {
           done_callback();
       }

       forEach(values,
               function(element) {
                   var invoked = false;
                   var elDone = function() {
                       if (invoked) {
                           return;
                       }

                       invoked = true;
                       remaining -= 1;

                       if (remaining === 0) {
                           done_callback();
                       }
                   };

                   iter_callback(element, elDone);
               });
   }

   function merge(a,b)
   {
       var rv = {};
       var p;
       for (p in a) {
           rv[p] = a[p];
       }
       for (p in b) {
           rv[p] = b[p];
       }
       return rv;
   }

   function expose(object, name)
   {
       var components = name.split(".");
       var target = global_scope;
       for (var i = 0; i < components.length - 1; i++) {
           if (!(components[i] in target)) {
               target[components[i]] = {};
           }
           target = target[components[i]];
       }
       target[components[components.length - 1]] = object;
   }

   function is_same_origin(w) {
       try {
           'random_prop' in w;
           return true;
       } catch (e) {
           return false;
       }
   }

   /** Returns the 'src' URL of the first <script> tag in the page to include the file 'testharness.js'. */
   function get_script_url()
   {
       if (!('document' in global_scope)) {
           return undefined;
       }

       var scripts = document.getElementsByTagName("script");
       for (var i = 0; i < scripts.length; i++) {
           var src;
           if (scripts[i].src) {
               src = scripts[i].src;
           } else if (scripts[i].href) {
               //SVG case
               src = scripts[i].href.baseVal;
           }

           var matches = src && src.match(/^(.*\/|)testharness\.js$/);
           if (matches) {
               return src;
           }
       }
       return undefined;
   }

   /** Returns the <title> or filename or "Untitled" */
   function get_title()
   {
       if ('document' in global_scope) {
           //Don't use document.title to work around an Opera/Presto bug in XHTML documents
           var title = document.getElementsByTagName("title")[0];
           if (title && title.firstChild && title.firstChild.data) {
               return title.firstChild.data;
           }
       }
       if ('META_TITLE' in global_scope && META_TITLE) {
           return META_TITLE;
       }
       if ('location' in global_scope && 'pathname' in location) {
           var filename = location.pathname.substring(location.pathname.lastIndexOf('/') + 1);
           return filename.substring(0, filename.indexOf('.'));
       }
       return "Untitled";
   }

   /** Fetches a JSON resource and parses it */
   async function fetch_json(resource) {
       const response = await fetch(resource);
       return await response.json();
   }
   if (!global_scope.GLOBAL || !global_scope.GLOBAL.isShadowRealm()) {
       expose(fetch_json, 'fetch_json');
   }

   /**
    * Setup globals
    */

   var tests = new Tests();

   if (global_scope.addEventListener) {
       var error_handler = function(error, message, stack) {
           var optional_unsupported = error instanceof OptionalFeatureUnsupportedError;
           if (tests.file_is_test) {
               var test = tests.tests[0];
               if (test.phase >= test.phases.HAS_RESULT) {
                   return;
               }
               var status = optional_unsupported ? test.PRECONDITION_FAILED : test.FAIL;
               test.set_status(status, message, stack);
               test.phase = test.phases.HAS_RESULT;
           } else if (!tests.allow_uncaught_exception) {
               var status = optional_unsupported ? tests.status.PRECONDITION_FAILED : tests.status.ERROR;
               tests.status.status = status;
               tests.status.message = message;
               tests.status.stack = stack;
           }

           // Do not transition to the "complete" phase if the test has been
           // configured to allow uncaught exceptions. This gives the test an
           // opportunity to define subtests based on the exception reporting
           // behavior.
           if (!tests.allow_uncaught_exception) {
               done();
           }
       };

       addEventListener("error", function(e) {
           var message = e.message;
           var stack;
           if (e.error && e.error.stack) {
               stack = e.error.stack;
           } else {
               stack = e.filename + ":" + e.lineno + ":" + e.colno;
           }
           error_handler(e.error, message, stack);
       }, false);

       addEventListener("unhandledrejection", function(e) {
           var message;
           if (e.reason && e.reason.message) {
               message = "Unhandled rejection: " + e.reason.message;
           } else {
               message = "Unhandled rejection";
           }
           var stack;
           if (e.reason && e.reason.stack) {
               stack = e.reason.stack;
           }
           error_handler(e.reason, message, stack);
       }, false);
   }

   test_environment.on_tests_ready();

   /**
    * Stylesheet
    */
    var stylesheetContent = "\
html {\
   font-family:DejaVu Sans, Bitstream Vera Sans, Arial, Sans;\
}\
\
#log .warning,\
#log .warning a {\
 color: black;\
 background: yellow;\
}\
\
#log .error,\
#log .error a {\
 color: white;\
 background: red;\
}\
\
section#summary {\
   margin-bottom:1em;\
}\
\
table#results {\
   border-collapse:collapse;\
   table-layout:fixed;\
   width:100%;\
}\
\
table#results > thead > tr > th:first-child,\
table#results > tbody > tr > td:first-child {\
   width:8em;\
}\
\
table#results > thead > tr > th:last-child,\
table#results > thead > tr > td:last-child {\
   width:50%;\
}\
\
table#results.assertions > thead > tr > th:last-child,\
table#results.assertions > tbody > tr > td:last-child {\
   width:35%;\
}\
\
table#results > thead > tr > th {\
   padding:0;\
   padding-bottom:0.5em;\
   border-bottom:medium solid black;\
}\
\
table#results > tbody > tr> td {\
   padding:1em;\
   padding-bottom:0.5em;\
   border-bottom:thin solid black;\
}\
\
.pass {\
   color:green;\
}\
\
.fail {\
   color:red;\
}\
\
tr.timeout {\
   color:red;\
}\
\
tr.notrun {\
   color:blue;\
}\
\
tr.optionalunsupported {\
   color:blue;\
}\
\
.ok {\
   color:green;\
}\
\
.error {\
   color:red;\
}\
\
.pass, .fail, .timeout, .notrun, .optionalunsupported .ok, .timeout, .error {\
   font-variant:small-caps;\
}\
\
table#results span {\
   display:block;\
}\
\
table#results span.expected {\
   font-family:DejaVu Sans Mono, Bitstream Vera Sans Mono, Monospace;\
   white-space:pre;\
}\
\
table#results span.actual {\
   font-family:DejaVu Sans Mono, Bitstream Vera Sans Mono, Monospace;\
   white-space:pre;\
}\
";

})(self);
// vim: set expandtab shiftwidth=4 tabstop=4: