mocking_bit_gen.h (9364B)
1 // Copyright 2018 The Abseil Authors. 2 // 3 // Licensed under the Apache License, Version 2.0 (the "License"); 4 // you may not use this file except in compliance with the License. 5 // You may obtain a copy of the License at 6 // 7 // https://www.apache.org/licenses/LICENSE-2.0 8 // 9 // Unless required by applicable law or agreed to in writing, software 10 // distributed under the License is distributed on an "AS IS" BASIS, 11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 12 // See the License for the specific language governing permissions and 13 // limitations under the License. 14 // 15 // ----------------------------------------------------------------------------- 16 // mocking_bit_gen.h 17 // ----------------------------------------------------------------------------- 18 // 19 // This file includes an `absl::MockingBitGen` class to use as a mock within the 20 // GoogleTest testing framework. Such a mock is useful to provide deterministic 21 // values as return values within (otherwise random) Abseil distribution 22 // functions. Such determinism within a mock is useful within testing frameworks 23 // to test otherwise indeterminate APIs. 24 // 25 // More information about the GoogleTest testing framework is available at 26 // https://github.com/google/googletest 27 28 #ifndef ABSL_RANDOM_MOCKING_BIT_GEN_H_ 29 #define ABSL_RANDOM_MOCKING_BIT_GEN_H_ 30 31 #include <memory> 32 #include <tuple> 33 #include <type_traits> 34 #include <utility> 35 36 #include "gmock/gmock.h" 37 #include "absl/base/config.h" 38 #include "absl/base/internal/fast_type_id.h" 39 #include "absl/container/flat_hash_map.h" 40 #include "absl/meta/type_traits.h" 41 #include "absl/random/internal/mock_helpers.h" 42 #include "absl/random/random.h" 43 #include "absl/utility/utility.h" 44 45 namespace absl { 46 ABSL_NAMESPACE_BEGIN 47 48 class BitGenRef; 49 50 namespace random_internal { 51 template <typename> 52 struct DistributionCaller; 53 class MockHelpers; 54 } // namespace random_internal 55 56 // MockingBitGen 57 // 58 // `absl::MockingBitGen` is a mock Uniform Random Bit Generator (URBG) class 59 // which can act in place of an `absl::BitGen` URBG within tests using the 60 // GoogleTest testing framework. 61 // 62 // Usage: 63 // 64 // Use an `absl::MockingBitGen` along with a mock distribution object (within 65 // mock_distributions.h) inside Googletest constructs such as ON_CALL(), 66 // EXPECT_TRUE(), etc. to produce deterministic results conforming to the 67 // distribution's API contract. 68 // 69 // Example: 70 // 71 // // Mock a call to an `absl::Bernoulli` distribution using Googletest 72 // absl::MockingBitGen bitgen; 73 // 74 // ON_CALL(absl::MockBernoulli(), Call(bitgen, 0.5)) 75 // .WillByDefault(testing::Return(true)); 76 // EXPECT_TRUE(absl::Bernoulli(bitgen, 0.5)); 77 // 78 // // Mock a call to an `absl::Uniform` distribution within Googletest 79 // absl::MockingBitGen bitgen; 80 // 81 // ON_CALL(absl::MockUniform<int>(), Call(bitgen, testing::_, testing::_)) 82 // .WillByDefault([] (int low, int high) { 83 // return low + (high - low) / 2; 84 // }); 85 // 86 // EXPECT_EQ(absl::Uniform<int>(gen, 0, 10), 5); 87 // EXPECT_EQ(absl::Uniform<int>(gen, 30, 40), 35); 88 // 89 // At this time, only mock distributions supplied within the Abseil random 90 // library are officially supported. 91 // 92 // EXPECT_CALL and ON_CALL need to be made within the same DLL component as 93 // the call to absl::Uniform and related methods, otherwise mocking will fail 94 // since the underlying implementation creates a type-specific pointer which 95 // will be distinct across different DLL boundaries. 96 // 97 class MockingBitGen { 98 public: 99 MockingBitGen() = default; 100 ~MockingBitGen() = default; 101 102 // URBG interface 103 using result_type = absl::BitGen::result_type; 104 105 static constexpr result_type(min)() { return (absl::BitGen::min)(); } 106 static constexpr result_type(max)() { return (absl::BitGen::max)(); } 107 result_type operator()() { return gen_(); } 108 109 private: 110 // GetMockFnType returns the testing::MockFunction for a result and tuple. 111 // This method only exists for type deduction and is otherwise unimplemented. 112 template <typename ResultT, typename... Args> 113 static auto GetMockFnType(ResultT, std::tuple<Args...>) 114 -> ::testing::MockFunction<ResultT(Args...)>; 115 116 // MockFnCaller is a helper method for use with absl::apply to 117 // apply an ArgTupleT to a compatible MockFunction. 118 // NOTE: MockFnCaller is essentially equivalent to the lambda: 119 // [fn](auto... args) { return fn->Call(std::move(args)...)} 120 // however that fails to build on some supported platforms. 121 template <typename MockFnType, typename ValidatorT, typename ResultT, 122 typename Tuple> 123 struct MockFnCaller; 124 125 // specialization for std::tuple. 126 template <typename MockFnType, typename ValidatorT, typename ResultT, 127 typename... Args> 128 struct MockFnCaller<MockFnType, ValidatorT, ResultT, std::tuple<Args...>> { 129 MockFnType* fn; 130 inline ResultT operator()(Args... args) { 131 ResultT result = fn->Call(args...); 132 ValidatorT::Validate(result, args...); 133 return result; 134 } 135 }; 136 137 // FunctionHolder owns a particular ::testing::MockFunction associated with 138 // a mocked type signature, and implement the type-erased Apply call, which 139 // applies type-erased arguments to the mock. 140 class FunctionHolder { 141 public: 142 virtual ~FunctionHolder() = default; 143 144 // Call is a dispatch function which converts the 145 // generic type-erased parameters into a specific mock invocation call. 146 virtual void Apply(/*ArgTupleT*/ void* args_tuple, 147 /*ResultT*/ void* result) = 0; 148 }; 149 150 template <typename MockFnType, typename ValidatorT, typename ResultT, 151 typename ArgTupleT> 152 class FunctionHolderImpl final : public FunctionHolder { 153 public: 154 void Apply(void* args_tuple, void* result) final { 155 // Requires tuple_args to point to a ArgTupleT, which is a 156 // std::tuple<Args...> used to invoke the mock function. Requires result 157 // to point to a ResultT, which is the result of the call. 158 *static_cast<ResultT*>(result) = absl::apply( 159 MockFnCaller<MockFnType, ValidatorT, ResultT, ArgTupleT>{&mock_fn_}, 160 *static_cast<ArgTupleT*>(args_tuple)); 161 } 162 163 MockFnType mock_fn_; 164 }; 165 166 // MockingBitGen::RegisterMock 167 // 168 // RegisterMock<ResultT, ArgTupleT>(FastTypeIdType) is the main extension 169 // point for extending the MockingBitGen framework. It provides a mechanism to 170 // install a mock expectation for a function like ResultT(Args...) keyed by 171 // type_idex onto the MockingBitGen context. The key is that the type_index 172 // used to register must match the type index used to call the mock. 173 // 174 // The returned MockFunction<...> type can be used to setup additional 175 // distribution parameters of the expectation. 176 template <typename ResultT, typename ArgTupleT, typename SelfT, 177 typename ValidatorT> 178 auto RegisterMock(SelfT&, base_internal::FastTypeIdType type, ValidatorT) 179 -> decltype(GetMockFnType(std::declval<ResultT>(), 180 std::declval<ArgTupleT>()))& { 181 using MockFnType = decltype(GetMockFnType(std::declval<ResultT>(), 182 std::declval<ArgTupleT>())); 183 184 using WrappedFnType = absl::conditional_t< 185 std::is_same<SelfT, ::testing::NiceMock<MockingBitGen>>::value, 186 ::testing::NiceMock<MockFnType>, 187 absl::conditional_t< 188 std::is_same<SelfT, ::testing::NaggyMock<MockingBitGen>>::value, 189 ::testing::NaggyMock<MockFnType>, 190 absl::conditional_t< 191 std::is_same<SelfT, 192 ::testing::StrictMock<MockingBitGen>>::value, 193 ::testing::StrictMock<MockFnType>, MockFnType>>>; 194 195 using ImplT = 196 FunctionHolderImpl<WrappedFnType, ValidatorT, ResultT, ArgTupleT>; 197 auto& mock = mocks_[type]; 198 if (!mock) { 199 mock = absl::make_unique<ImplT>(); 200 } 201 return static_cast<ImplT*>(mock.get())->mock_fn_; 202 } 203 204 // MockingBitGen::InvokeMock 205 // 206 // bool InvokeMock(key_id, args_tuple*, result*) is the entrypoint 207 // for invoking mocks registered on MockingBitGen. 208 // 209 // When no mocks are registered on the provided FastTypeIdType, returns false. 210 // Otherwise attempts to invoke the mock function ResultT(Args...) that 211 // was previously registered via the type_index. 212 // Requires tuple_args to point to a ArgTupleT, which is a std::tuple<Args...> 213 // used to invoke the mock function. 214 // Requires result to point to a ResultT, which is the result of the call. 215 inline bool InvokeMock(base_internal::FastTypeIdType key_id, void* args_tuple, 216 void* result) { 217 // Trigger a mock, if there exists one that matches `param`. 218 auto it = mocks_.find(key_id); 219 if (it == mocks_.end()) return false; 220 it->second->Apply(args_tuple, result); 221 return true; 222 } 223 224 absl::flat_hash_map<base_internal::FastTypeIdType, 225 std::unique_ptr<FunctionHolder>> 226 mocks_; 227 absl::BitGen gen_; 228 229 template <typename> 230 friend struct ::absl::random_internal::DistributionCaller; // for InvokeMock 231 friend class ::absl::BitGenRef; // for InvokeMock 232 friend class ::absl::random_internal::MockHelpers; // for RegisterMock, 233 // InvokeMock 234 }; 235 236 ABSL_NAMESPACE_END 237 } // namespace absl 238 239 #endif // ABSL_RANDOM_MOCKING_BIT_GEN_H_