// Copyright 2018 The Abseil Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
// -----------------------------------------------------------------------------
// mocking_bit_gen.h
// -----------------------------------------------------------------------------
//
// This file includes an `absl::MockingBitGen` class to use as a mock within the
// Googletest testing framework. Such a mock is useful to provide deterministic
// values as return values within (otherwise random) Abseil distribution
// functions. Such determinism within a mock is useful within testing frameworks
// to test otherwise indeterminate APIs.
//
// More information about the Googletest testing framework is available at
// https://github.com/google/googletest
#ifndef ABSL_RANDOM_MOCKING_BIT_GEN_H_
#define ABSL_RANDOM_MOCKING_BIT_GEN_H_
#include <iterator>
#include <limits>
#include <memory>
#include <tuple>
#include <type_traits>
#include <typeindex>
#include <typeinfo>
#include <utility>
#include "gmock/gmock.h"
#include "gtest/gtest.h"
#include "absl/container/flat_hash_map.h"
#include "absl/meta/type_traits.h"
#include "absl/random/distributions.h"
#include "absl/random/internal/distribution_caller.h"
#include "absl/random/internal/mocking_bit_gen_base.h"
#include "absl/strings/str_cat.h"
#include "absl/strings/str_join.h"
#include "absl/types/span.h"
#include "absl/types/variant.h"
#include "absl/utility/utility.h"
namespace absl {
ABSL_NAMESPACE_BEGIN
namespace random_internal {
template <typename, typename>
struct MockSingleOverload;
} // namespace random_internal
// MockingBitGen
//
// `absl::MockingBitGen` is a mock Uniform Random Bit Generator (URBG) class
// which can act in place of an `absl::BitGen` URBG within tests using the
// Googletest testing framework.
//
// Usage:
//
// Use an `absl::MockingBitGen` along with a mock distribution object (within
// mock_distributions.h) inside Googletest constructs such as ON_CALL(),
// EXPECT_TRUE(), etc. to produce deterministic results conforming to the
// distribution's API contract.
//
// Example:
//
// // Mock a call to an `absl::Bernoulli` distribution using Googletest
// absl::MockingBitGen bitgen;
//
// ON_CALL(absl::MockBernoulli(), Call(bitgen, 0.5))
// .WillByDefault(testing::Return(true));
// EXPECT_TRUE(absl::Bernoulli(bitgen, 0.5));
//
// // Mock a call to an `absl::Uniform` distribution within Googletest
// absl::MockingBitGen bitgen;
//
// ON_CALL(absl::MockUniform<int>(), Call(bitgen, testing::_, testing::_))
// .WillByDefault([] (int low, int high) {
// return (low + high) / 2;
// });
//
// EXPECT_EQ(absl::Uniform<int>(gen, 0, 10), 5);
// EXPECT_EQ(absl::Uniform<int>(gen, 30, 40), 35);
//
// At this time, only mock distributions supplied within the Abseil random
// library are officially supported.
//
class MockingBitGen : public absl::random_internal::MockingBitGenBase {
public:
MockingBitGen() {}
~MockingBitGen() override;
private:
template <typename DistrT, typename... Args>
using MockFnType =
::testing::MockFunction<typename DistrT::result_type(Args...)>;
// MockingBitGen::Register
//
// Register<DistrT, FormatT, ArgTupleT> is the main extension point for
// extending the MockingBitGen framework. It provides a mechanism to install a
// mock expectation for the distribution `distr_t` onto the MockingBitGen
// context.
//
// The returned MockFunction<...> type can be used to setup additional
// distribution parameters of the expectation.
template <typename DistrT, typename... Args, typename... Ms>
decltype(std::declval<MockFnType<DistrT, Args...>>().gmock_Call(
std::declval<Ms>()...))
Register(Ms&&... matchers) {
auto& mock =
mocks_[std::type_index(GetTypeId<DistrT, std::tuple<Args...>>())];
if (!mock.mock_fn) {
auto* mock_fn = new MockFnType<DistrT, Args...>;
mock.mock_fn = mock_fn;
mock.match_impl = &MatchImpl<DistrT, Args...>;
deleters_.emplace_back([mock_fn] { delete mock_fn; });
}
return static_cast<MockFnType<DistrT, Args...>*>(mock.mock_fn)
->gmock_Call(std::forward<Ms>(matchers)...);
}
mutable std::vector<std::function<void()>> deleters_;
using match_impl_fn = void (*)(void* mock_fn, void* t_erased_dist_args,
void* t_erased_result);
struct MockData {
void* mock_fn = nullptr;
match_impl_fn match_impl = nullptr;
};
mutable absl::flat_hash_map<std::type_index, MockData> mocks_;
template <typename DistrT, typename... Args>
static void MatchImpl(void* mock_fn, void* dist_args, void* result) {
using result_type = typename DistrT::result_type;
*static_cast<result_type*>(result) = absl::apply(
[mock_fn](Args... args) -> result_type {
return (*static_cast<MockFnType<DistrT, Args...>*>(mock_fn))
.Call(std::move(args)...);
},
*static_cast<std::tuple<Args...>*>(dist_args));
}
// Looks for an appropriate mock - Returns the mocked result if one is found.
// Otherwise, returns a random value generated by the underlying URBG.
bool CallImpl(const std::type_info& key_type, void* dist_args,
void* result) override {
// Trigger a mock, if there exists one that matches `param`.
auto it = mocks_.find(std::type_index(key_type));
if (it == mocks_.end()) return false;
auto* mock_data = static_cast<MockData*>(&it->second);
mock_data->match_impl(mock_data->mock_fn, dist_args, result);
return true;
}
template <typename, typename>
friend struct ::absl::random_internal::MockSingleOverload;
friend struct ::absl::random_internal::DistributionCaller<
absl::MockingBitGen>;
};
// -----------------------------------------------------------------------------
// Implementation Details Only Below
// -----------------------------------------------------------------------------
namespace random_internal {
template <>
struct DistributionCaller<absl::MockingBitGen> {
template <typename DistrT, typename FormatT, typename... Args>
static typename DistrT::result_type Call(absl::MockingBitGen* gen,
Args&&... args) {
return gen->template Call<DistrT, FormatT>(std::forward<Args>(args)...);
}
};
} // namespace random_internal
ABSL_NAMESPACE_END
} // namespace absl
#endif // ABSL_RANDOM_MOCKING_BIT_GEN_H_
