228 lines
8.7 KiB
C++
228 lines
8.7 KiB
C++
// Copyright 2018 The Abseil Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// https://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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//
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// -----------------------------------------------------------------------------
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// mocking_bit_gen.h
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// -----------------------------------------------------------------------------
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//
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// This file includes an `absl::MockingBitGen` class to use as a mock within the
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// Googletest testing framework. Such a mock is useful to provide deterministic
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// values as return values within (otherwise random) Abseil distribution
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// functions. Such determinism within a mock is useful within testing frameworks
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// to test otherwise indeterminate APIs.
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//
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// More information about the Googletest testing framework is available at
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// https://github.com/google/googletest
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#ifndef ABSL_RANDOM_MOCKING_BIT_GEN_H_
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#define ABSL_RANDOM_MOCKING_BIT_GEN_H_
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#include <iterator>
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#include <limits>
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#include <memory>
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#include <tuple>
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#include <type_traits>
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#include <utility>
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#include "gmock/gmock.h"
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#include "gtest/gtest.h"
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#include "absl/base/internal/fast_type_id.h"
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#include "absl/container/flat_hash_map.h"
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#include "absl/meta/type_traits.h"
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#include "absl/random/distributions.h"
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#include "absl/random/internal/distribution_caller.h"
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#include "absl/random/random.h"
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#include "absl/strings/str_cat.h"
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#include "absl/strings/str_join.h"
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#include "absl/types/span.h"
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#include "absl/types/variant.h"
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#include "absl/utility/utility.h"
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namespace absl {
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ABSL_NAMESPACE_BEGIN
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namespace random_internal {
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template <typename>
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struct DistributionCaller;
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class MockHelpers;
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} // namespace random_internal
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class BitGenRef;
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// MockingBitGen
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//
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// `absl::MockingBitGen` is a mock Uniform Random Bit Generator (URBG) class
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// which can act in place of an `absl::BitGen` URBG within tests using the
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// Googletest testing framework.
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//
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// Usage:
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//
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// Use an `absl::MockingBitGen` along with a mock distribution object (within
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// mock_distributions.h) inside Googletest constructs such as ON_CALL(),
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// EXPECT_TRUE(), etc. to produce deterministic results conforming to the
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// distribution's API contract.
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//
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// Example:
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//
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// // Mock a call to an `absl::Bernoulli` distribution using Googletest
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// absl::MockingBitGen bitgen;
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//
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// ON_CALL(absl::MockBernoulli(), Call(bitgen, 0.5))
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// .WillByDefault(testing::Return(true));
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// EXPECT_TRUE(absl::Bernoulli(bitgen, 0.5));
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//
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// // Mock a call to an `absl::Uniform` distribution within Googletest
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// absl::MockingBitGen bitgen;
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//
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// ON_CALL(absl::MockUniform<int>(), Call(bitgen, testing::_, testing::_))
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// .WillByDefault([] (int low, int high) {
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// return (low + high) / 2;
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// });
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//
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// EXPECT_EQ(absl::Uniform<int>(gen, 0, 10), 5);
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// EXPECT_EQ(absl::Uniform<int>(gen, 30, 40), 35);
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//
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// At this time, only mock distributions supplied within the Abseil random
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// library are officially supported.
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//
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// EXPECT_CALL and ON_CALL need to be made within the same DLL component as
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// the call to absl::Uniform and related methods, otherwise mocking will fail
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// since the underlying implementation creates a type-specific pointer which
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// will be distinct across different DLL boundaries.
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//
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class MockingBitGen {
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public:
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MockingBitGen() = default;
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~MockingBitGen() {
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for (const auto& del : deleters_) del();
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}
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// URBG interface
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using result_type = absl::BitGen::result_type;
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static constexpr result_type(min)() { return (absl::BitGen::min)(); }
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static constexpr result_type(max)() { return (absl::BitGen::max)(); }
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result_type operator()() { return gen_(); }
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private:
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using match_impl_fn = void (*)(void* mock_fn, void* t_erased_arg_tuple,
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void* t_erased_result);
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struct MockData {
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void* mock_fn = nullptr;
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match_impl_fn match_impl = nullptr;
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};
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// GetMockFnType returns the testing::MockFunction for a result and tuple.
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// This method only exists for type deduction and is otherwise unimplemented.
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template <typename ResultT, typename... Args>
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static auto GetMockFnType(ResultT, std::tuple<Args...>)
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-> ::testing::MockFunction<ResultT(Args...)>;
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// MockFnCaller is a helper method for use with absl::apply to
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// apply an ArgTupleT to a compatible MockFunction.
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// NOTE: MockFnCaller is essentially equivalent to the lambda:
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// [fn](auto... args) { return fn->Call(std::move(args)...)}
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// however that fails to build on some supported platforms.
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template <typename ResultT, typename MockFnType, typename Tuple>
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struct MockFnCaller;
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// specialization for std::tuple.
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template <typename ResultT, typename MockFnType, typename... Args>
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struct MockFnCaller<ResultT, MockFnType, std::tuple<Args...>> {
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MockFnType* fn;
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inline ResultT operator()(Args... args) {
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return fn->Call(std::move(args)...);
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}
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};
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// MockingBitGen::RegisterMock
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//
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// RegisterMock<ResultT, ArgTupleT>(FastTypeIdType) is the main extension
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// point for extending the MockingBitGen framework. It provides a mechanism to
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// install a mock expectation for a function like ResultT(Args...) keyed by
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// type_idex onto the MockingBitGen context. The key is that the type_index
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// used to register must match the type index used to call the mock.
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//
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// The returned MockFunction<...> type can be used to setup additional
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// distribution parameters of the expectation.
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template <typename ResultT, typename ArgTupleT>
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auto RegisterMock(base_internal::FastTypeIdType type)
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-> decltype(GetMockFnType(std::declval<ResultT>(),
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std::declval<ArgTupleT>()))& {
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using MockFnType = decltype(
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GetMockFnType(std::declval<ResultT>(), std::declval<ArgTupleT>()));
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auto& mock = mocks_[type];
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if (!mock.mock_fn) {
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auto* mock_fn = new MockFnType;
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mock.mock_fn = mock_fn;
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mock.match_impl = &MatchImpl<ResultT, ArgTupleT>;
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deleters_.emplace_back([mock_fn] { delete mock_fn; });
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}
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return *static_cast<MockFnType*>(mock.mock_fn);
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}
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// MockingBitGen::MatchImpl<> is a dispatch function which converts the
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// generic type-erased parameters into a specific mock invocation call.
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// Requires tuple_args to point to a ArgTupleT, which is a std::tuple<Args...>
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// used to invoke the mock function.
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// Requires result to point to a ResultT, which is the result of the call.
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template <typename ResultT, typename ArgTupleT>
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static void MatchImpl(/*MockFnType<ResultT, Args...>*/ void* mock_fn,
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/*ArgTupleT*/ void* args_tuple,
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/*ResultT*/ void* result) {
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using MockFnType = decltype(
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GetMockFnType(std::declval<ResultT>(), std::declval<ArgTupleT>()));
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*static_cast<ResultT*>(result) = absl::apply(
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MockFnCaller<ResultT, MockFnType, ArgTupleT>{
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static_cast<MockFnType*>(mock_fn)},
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*static_cast<ArgTupleT*>(args_tuple));
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}
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// MockingBitGen::InvokeMock
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//
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// InvokeMock(FastTypeIdType, args, result) is the entrypoint for invoking
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// mocks registered on MockingBitGen.
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//
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// When no mocks are registered on the provided FastTypeIdType, returns false.
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// Otherwise attempts to invoke the mock function ResultT(Args...) that
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// was previously registered via the type_index.
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// Requires tuple_args to point to a ArgTupleT, which is a std::tuple<Args...>
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// used to invoke the mock function.
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// Requires result to point to a ResultT, which is the result of the call.
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inline bool InvokeMock(base_internal::FastTypeIdType type, void* args_tuple,
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void* result) {
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// Trigger a mock, if there exists one that matches `param`.
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auto it = mocks_.find(type);
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if (it == mocks_.end()) return false;
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auto* mock_data = static_cast<MockData*>(&it->second);
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mock_data->match_impl(mock_data->mock_fn, args_tuple, result);
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return true;
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}
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absl::flat_hash_map<base_internal::FastTypeIdType, MockData> mocks_;
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std::vector<std::function<void()>> deleters_;
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absl::BitGen gen_;
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template <typename>
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friend struct ::absl::random_internal::DistributionCaller; // for InvokeMock
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friend class ::absl::BitGenRef; // for InvokeMock
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friend class ::absl::random_internal::MockHelpers; // for RegisterMock,
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// InvokeMock
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};
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ABSL_NAMESPACE_END
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} // namespace absl
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#endif // ABSL_RANDOM_MOCKING_BIT_GEN_H_
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