Practical example for Dependency Injection and 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

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();
}
*/`