summaryrefslogtreecommitdiff
path: root/absl/random/mocking_bit_gen.h
blob: 36cef91113e365c9169da641f70c2b0592e024bb (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
// 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_