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 <iterator> 32 #include <limits> 33 #include <memory> 34 #include <tuple> 35 #include <type_traits> 36 #include <utility> 37 38 #include "gmock/gmock.h" 39 #include "gtest/gtest.h" 40 #include "absl/base/internal/fast_type_id.h" 41 #include "absl/container/flat_hash_map.h" 42 #include "absl/meta/type_traits.h" 43 #include "absl/random/distributions.h" 44 #include "absl/random/internal/distribution_caller.h" 45 #include "absl/random/random.h" 46 #include "absl/strings/str_cat.h" 47 #include "absl/strings/str_join.h" 48 #include "absl/types/span.h" 49 #include "absl/types/variant.h" 50 #include "absl/utility/utility.h" 51 52 namespace absl { 53 ABSL_NAMESPACE_BEGIN 54 55 namespace random_internal { 56 template <typename> 57 struct DistributionCaller; 58 class MockHelpers; 59 60 } // namespace random_internal 61 class BitGenRef; 62 63 // MockingBitGen 64 // 65 // `absl::MockingBitGen` is a mock Uniform Random Bit Generator (URBG) class 66 // which can act in place of an `absl::BitGen` URBG within tests using the 67 // Googletest testing framework. 68 // 69 // Usage: 70 // 71 // Use an `absl::MockingBitGen` along with a mock distribution object (within 72 // mock_distributions.h) inside Googletest constructs such as ON_CALL(), 73 // EXPECT_TRUE(), etc. to produce deterministic results conforming to the 74 // distribution's API contract. 75 // 76 // Example: 77 // 78 // // Mock a call to an `absl::Bernoulli` distribution using Googletest 79 // absl::MockingBitGen bitgen; 80 // 81 // ON_CALL(absl::MockBernoulli(), Call(bitgen, 0.5)) 82 // .WillByDefault(testing::Return(true)); 83 // EXPECT_TRUE(absl::Bernoulli(bitgen, 0.5)); 84 // 85 // // Mock a call to an `absl::Uniform` distribution within Googletest 86 // absl::MockingBitGen bitgen; 87 // 88 // ON_CALL(absl::MockUniform<int>(), Call(bitgen, testing::_, testing::_)) 89 // .WillByDefault([] (int low, int high) { 90 // return low + (high - low) / 2; 91 // }); 92 // 93 // EXPECT_EQ(absl::Uniform<int>(gen, 0, 10), 5); 94 // EXPECT_EQ(absl::Uniform<int>(gen, 30, 40), 35); 95 // 96 // At this time, only mock distributions supplied within the Abseil random 97 // library are officially supported. 98 // 99 // EXPECT_CALL and ON_CALL need to be made within the same DLL component as 100 // the call to absl::Uniform and related methods, otherwise mocking will fail 101 // since the underlying implementation creates a type-specific pointer which 102 // will be distinct across different DLL boundaries. 103 // 104 class MockingBitGen { 105 public: 106 MockingBitGen() = default; 107 ~MockingBitGen() = default; 108 109 // URBG interface 110 using result_type = absl::BitGen::result_type; 111 result_type(min)112 static constexpr result_type(min)() { return (absl::BitGen::min)(); } result_type(max)113 static constexpr result_type(max)() { return (absl::BitGen::max)(); } operator()114 result_type operator()() { return gen_(); } 115 116 private: 117 // GetMockFnType returns the testing::MockFunction for a result and tuple. 118 // This method only exists for type deduction and is otherwise unimplemented. 119 template <typename ResultT, typename... Args> 120 static auto GetMockFnType(ResultT, std::tuple<Args...>) 121 -> ::testing::MockFunction<ResultT(Args...)>; 122 123 // MockFnCaller is a helper method for use with absl::apply to 124 // apply an ArgTupleT to a compatible MockFunction. 125 // NOTE: MockFnCaller is essentially equivalent to the lambda: 126 // [fn](auto... args) { return fn->Call(std::move(args)...)} 127 // however that fails to build on some supported platforms. 128 template <typename MockFnType, typename ResultT, typename Tuple> 129 struct MockFnCaller; 130 131 // specialization for std::tuple. 132 template <typename MockFnType, typename ResultT, typename... Args> 133 struct MockFnCaller<MockFnType, ResultT, std::tuple<Args...>> { 134 MockFnType* fn; 135 inline ResultT operator()(Args... args) { 136 return fn->Call(std::move(args)...); 137 } 138 }; 139 140 // FunctionHolder owns a particular ::testing::MockFunction associated with 141 // a mocked type signature, and implement the type-erased Apply call, which 142 // applies type-erased arguments to the mock. 143 class FunctionHolder { 144 public: 145 virtual ~FunctionHolder() = default; 146 147 // Call is a dispatch function which converts the 148 // generic type-erased parameters into a specific mock invocation call. 149 virtual void Apply(/*ArgTupleT*/ void* args_tuple, 150 /*ResultT*/ void* result) = 0; 151 }; 152 153 template <typename MockFnType, typename ResultT, typename ArgTupleT> 154 class FunctionHolderImpl final : public FunctionHolder { 155 public: 156 void Apply(void* args_tuple, void* result) override { 157 // Requires tuple_args to point to a ArgTupleT, which is a 158 // std::tuple<Args...> used to invoke the mock function. Requires result 159 // to point to a ResultT, which is the result of the call. 160 *static_cast<ResultT*>(result) = 161 absl::apply(MockFnCaller<MockFnType, ResultT, ArgTupleT>{&mock_fn_}, 162 *static_cast<ArgTupleT*>(args_tuple)); 163 } 164 165 MockFnType mock_fn_; 166 }; 167 168 // MockingBitGen::RegisterMock 169 // 170 // RegisterMock<ResultT, ArgTupleT>(FastTypeIdType) is the main extension 171 // point for extending the MockingBitGen framework. It provides a mechanism to 172 // install a mock expectation for a function like ResultT(Args...) keyed by 173 // type_idex onto the MockingBitGen context. The key is that the type_index 174 // used to register must match the type index used to call the mock. 175 // 176 // The returned MockFunction<...> type can be used to setup additional 177 // distribution parameters of the expectation. 178 template <typename ResultT, typename ArgTupleT, typename SelfT> 179 auto RegisterMock(SelfT&, base_internal::FastTypeIdType type) 180 -> decltype(GetMockFnType(std::declval<ResultT>(), 181 std::declval<ArgTupleT>()))& { 182 using MockFnType = decltype(GetMockFnType(std::declval<ResultT>(), 183 std::declval<ArgTupleT>())); 184 185 using WrappedFnType = absl::conditional_t< 186 std::is_same<SelfT, ::testing::NiceMock<absl::MockingBitGen>>::value, 187 ::testing::NiceMock<MockFnType>, 188 absl::conditional_t< 189 std::is_same<SelfT, 190 ::testing::NaggyMock<absl::MockingBitGen>>::value, 191 ::testing::NaggyMock<MockFnType>, 192 absl::conditional_t< 193 std::is_same<SelfT, 194 ::testing::StrictMock<absl::MockingBitGen>>::value, 195 ::testing::StrictMock<MockFnType>, MockFnType>>>; 196 197 using ImplT = FunctionHolderImpl<WrappedFnType, ResultT, ArgTupleT>; 198 auto& mock = mocks_[type]; 199 if (!mock) { 200 mock = absl::make_unique<ImplT>(); 201 } 202 return static_cast<ImplT*>(mock.get())->mock_fn_; 203 } 204 205 // MockingBitGen::InvokeMock 206 // 207 // InvokeMock(FastTypeIdType, args, result) is the entrypoint for invoking 208 // mocks registered on MockingBitGen. 209 // 210 // When no mocks are registered on the provided FastTypeIdType, returns false. 211 // Otherwise attempts to invoke the mock function ResultT(Args...) that 212 // was previously registered via the type_index. 213 // Requires tuple_args to point to a ArgTupleT, which is a std::tuple<Args...> 214 // used to invoke the mock function. 215 // Requires result to point to a ResultT, which is the result of the call. 216 inline bool InvokeMock(base_internal::FastTypeIdType type, void* args_tuple, 217 void* result) { 218 // Trigger a mock, if there exists one that matches `param`. 219 auto it = mocks_.find(type); 220 if (it == mocks_.end()) return false; 221 it->second->Apply(args_tuple, result); 222 return true; 223 } 224 225 absl::flat_hash_map<base_internal::FastTypeIdType, 226 std::unique_ptr<FunctionHolder>> 227 mocks_; 228 absl::BitGen gen_; 229 230 template <typename> 231 friend struct ::absl::random_internal::DistributionCaller; // for InvokeMock 232 friend class ::absl::BitGenRef; // for InvokeMock 233 friend class ::absl::random_internal::MockHelpers; // for RegisterMock, 234 // InvokeMock 235 }; 236 237 ABSL_NAMESPACE_END 238 } // namespace absl 239 240 #endif // ABSL_RANDOM_MOCKING_BIT_GEN_H_ 241