依赖注入的实际例子和 mocking with Googlemock

Question

I'm looking for a simple complete cut and paste example for Dependency Injection and mocking using Googlemock. I have found several theoretical discussion about the issue with code snippets that explains how it works but wasn't able to find a complete running example to cut and paste and try. Is there something available?

Answer 1

To understand how it works with Googlemock I have made this complete example that I would like to share with other beginners to the topic. According to other Q&A theoretical background is assumed. I run it on a Debian Bullseye system.

There is a class Mylib in a fictional library that method just returns 123 . Under test it is mocked to return 456 . The real class and the mocking class are both inherit from an interface class. This ensures that the different objects that are injected by the injector ( TEST(..){..} macro) to the application Myapp , have the same method calls. Here is the example:

~$ 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();
}

I compiled it with:

~$ /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

When executing the test it should look like this:

~$ ./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.

Answer 2

Ingo's example using std::shared_ptr.

// Ingo's answer to Dependency Injection and mocking modified to
// use std::shared_ptr.

#include <iostream>
#include <memory>

#include "gmock/gmock.h"
#include "gtest/gtest.h"

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

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

using MyLibPtr = std::shared_ptr<MylibInterface>;

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;
  MyLibPtr m_mylib;

 public:
  Myapp(MyLibPtr 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
  Myapp myapp(std::make_shared<Mylib>());
  std::cout << "  real ";
  EXPECT_TRUE(myapp.func());

  // inject a mocked mylib object to myapp
  //MylibMock mylib_mock;
  auto lp = std::make_shared<MylibMock>();
  Myapp myapp_mock( lp );

  //EXPECT_CALL(mylib_mock, func())
  EXPECT_CALL( *lp, 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();
}
*/`