使用 Googlemock 进行依赖注入和模拟的实用示例答案

【问题标题】：Practical example for Dependency Injection and mocking with Googlemock使用 Googlemock 进行依赖注入和模拟的实用示例
【发布时间】：2021-03-13 16:08:50
【问题描述】：

我正在寻找一个简单的完整剪切和粘贴示例，用于使用 Googlemock 进行依赖注入和模拟。我发现了几个关于代码 sn-ps 问题的理论讨论，这些讨论解释了它是如何工作的，但无法找到一个完整的运行示例来剪切和粘贴并尝试。有货吗？

【问题讨论】：

标签： c++ unit-testing dependency-injection googlemock

【解决方案1】：

为了了解它如何与 Googlemock 一起工作，我制作了这个完整的示例，我想与其他初学者分享该主题。根据其他问答理论背景假设。我在 Debian Bullseye 系统上运行它。

在一个虚构的库中有一个类Mylib，该方法只返回123。在测试中，它被模拟返回456。真实类和模拟类都继承自接口类。这确保了由注入器（TEST(..){..} 宏）注入到应用程序Myapp 的不同对象具有相同的方法调用。示例如下：

~$ cat test_myapp.cpp
#include "gtest/gtest.h"
#include "gmock/gmock.h"
#include <iostream>

class MylibInterface {
public:
    virtual ~MylibInterface() {}
    virtual int func() = 0;
};


class Mylib : public MylibInterface {
public:
    virtual ~Mylib() {}
    int func() override {
        return 123;
    }
};


class MylibMock : public MylibInterface {
public:
    virtual ~MylibMock() {}
    MOCK_METHOD(int, func, (), (override));
};


class Myapp {
    // this pointer will be injected by the injector either with pointing
    // to the real object or to the mock object. The interface ensures that both
    // objects have the same method calls.
    MylibInterface* m_mylib;

public:
    Myapp(MylibInterface* mylib) : m_mylib(mylib) {}

    bool func() {
        int ret = m_mylib->func();
        std::cout << "mylib.func returns: '" << ret << "'\n";
        return true;
    }
};


TEST(MylibTestSuite, mock_mylib_func)
// this test macro can be seen as the injector. It determins what object
// is injected to myapp.
{
    using ::testing::Return;

    // inject a real mylib object to myapp and exersize it
    Mylib mylib;
    Myapp myapp(&mylib);
    std::cout << "  real ";
    EXPECT_TRUE(myapp.func());

    // inject a mocked mylib object to myapp
    MylibMock mylib_mock;
    Myapp myapp_mock(&mylib_mock);
    EXPECT_CALL(mylib_mock, func())
        .WillOnce(Return(456));

    // and exersize it
    std::cout << "mocked ";
    EXPECT_TRUE(myapp_mock.func());
}


int main(int argc, char** argv) {
  ::testing::InitGoogleMock(&argc, argv);
  return RUN_ALL_TESTS();
}

我编译它：

~$ /usr/bin/g++ -std=c++11 -pedantic-errors -Wall -o test_myapp.a -I$BUILD_DIR/googletest-src/googletest/include -I$BUILD_DIR/googletest-src/googlemock/include test_myapp.cpp $BUILD_DIR/lib/libgtestd.a $BUILD_DIR/lib/libgmockd.a -lpthread

执行测试时应该如下所示：

~$ ./test_myapp.a
[==========] Running 1 test from 1 test suite.
[----------] Global test environment set-up.
[----------] 1 test from MylibTestSuite
[ RUN      ] MylibTestSuite.mock_mylib_func
  real mylib.func returns: '123'
mocked mylib.func returns: '456'
[       OK ] MylibTestSuite.mock_mylib_func (0 ms)
[----------] 1 test from MylibTestSuite (0 ms total)

[----------] Global test environment tear-down
[==========] 1 test from 1 test suite ran. (0 ms total)
[  PASSED  ] 1 test.

【讨论】：