Simple Mocking in C++

I’ve been working in C++ for a few months now – after three years we’ve been apart.
I always amazes me how simple things I took for granted do not exist (at least not out of the box) in C++, one of which are reflection.
Two weeks ago I needed to make sure that a method was called in a test, I could have used Google’s mocking framework but I needed simpler and quicker solution. I just wanted to know in a specific point at the test if a method was called.
Although C++ does not have reflection it does have macros (i.e. #Define) and I’ve utilized the C++ macros to create the following class:

#ifndef __TESTLISTENERBASE_H__
#define __TESTLISTENERBASE_H__

#include
#include

class TestListenerBase
{
protected:
void AddMethodCall(std::string methodName)
{
_methodsCalled.insert(methodName);
}

bool WasCalled(std::string methodName)
{
return _methodsCalled.count(methodName) > 0;
}
private:
std::unordered_set _methodsCalled;
};

#define REGISTER_METHOD(METHODNAME) \
void METHODNAME () override\
{ \
AddMethodCall(#METHODNAME); \
} \
bool METHODNAME##WasCalled() \
{ \
return WasCalled(#METHODNAME); \
}

#endif

By inheriting from the class above I could define the “mocked” methods, each method would have another method  auto-generated so I can test if the method was called.

#ifndef __MY_CLASS_MOCK__
#define __MY_CLASS_MOCK__

#include "TestListenerBase.h"
#include "MyClass.h"

class MyClassMock : public MyClass, public TestListenerBase
{
public:
REGISTER_METHOD(DoSomething);
};

#endif

Using this solution I needed to declare each method, the good news is that renaming the method would cause the mocked method name to change as well.

Using the new “mock object” is a simple as writing code:

#include "stdafx.h"
#include
#include "MyClassMock.h"

int _tmain(int argc, _TCHAR* argv[])
{
MyClassMock mock;

bool result = mock.DoSomethingWasCalled(); // return false

mock.DoSomething();

result = mock.DoSomethingWasCalled(); // result true

return 0;
}

That’s it – it’s not perfect but it works.

In case you like parameters in your method you’ll have to improve this example – it’s not hard and I know you’re up to the task.

Happy coding…

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