White-box testing - friends or preprocessor?

Question

So, imagine we have a class like this

class Testee
{
public:
   void Func()
private:
   void auxFunc()
};

and we want to do white-box unit-testing on it. Which do you think is a better approach? To declare the tester class a friend of the testee class? Or use the preprocessor like this:

  class Testee
    {
    public:
       void Func()
#ifndef UNITTEST_SYMBOL
    private:
#elif
    public:
#endif
       void auxFunc()
    };

and later in the testing file

#define UNITTEST_SYMBOL
#include "Testee.h"
#undef UNITTEST_SYMBOL

So, again, which do you think is a better approach? Or maybe you could suggest another approach. Thanks in advance.

Answer 1

How about:

#ifndef UNITTEST_SYMBOL
#define semiprivate private 
#else
#define semiprivate public
#endif

and declare your class like:

  class Testee
    {
    public:
       void Func()
    semiprivate:
       void auxFunc()
    };

or even, if you're daring enough, do #define private public when testing.

Answer 2

Using the friend method, the declaration would depend on the name of the test class, so if you ever change it's name the declaration has to be changed as well. Moreover I use Unittest++ so the actual test calss name is formed by a macro.

The method with the define is less hassle then. Also, I'd just put the define as a global compiler option instead of the way you show, for example

gcc -DUNIT_TESTING_ON

#ifdef UNIT_TESTING_ON
  public: //or protected maybe
#else
  private:
#endif

Anyone reading this would also see what the purpose is, this is more clear than having to look up the definition of the friend to see why exactly you made it a friend.

Answer 3

In the unit test file. You could try

#define private public
#include "Testee.h"

This is what I do, it means that there isn't anything related to unit testing within the header file. I find this very useful as I find it hard to follow when there are lots of #ifdef within my code.

I then have all my other header files before the #define