Calling private member of inherited class for unittest

Question

I'm trying to write a unittest but I'm running into some problems.

I've got a class which has an int to keep track of the current state. All classes that are inherited of this class can change the state by calling the protectedFunction.

class RandomClass
{
public:
  RandomClass()
  { 
    mState = 0; 
  }
protected:
  void protectedFunction()
  {
    ++mState;
  }
private:
  int mState;
  friend void UNITTEST_setMState(int state);
  friend int UNITTEST_getMState();
};

Now i'd like to write a unittest for this class. So I created a new class which inherits the previous class. To Properly test all the states I need to set the state, and I need to get the state to assert it. I've tried using a friend function but it does not seem to work.

class UnittestRandomClass : public RandomClass
{
public:
  void wrapperProtectedFunction()
  {
    protectedFunction();
  }

  void UNITTEST_setMState(int state)
  {
    this->mState = state; // Apparently not like this
  }

  int UNITTEST_getMState()
  {
    return this->mState; // Apparently not like this
  }
};

int main() {
  UnittestRandomClass ut;
  ut.UNITTEST_setMState(1);
  ut.wrapperProtectedFunction();
  int res = ut.UNITTEST_getMState();
  ASSERT_EQ(res, 2);
}

I seem to be doing something wrong, as the mState still appears to be private and thus I'm getting an inaccessible error. I've also tried calling it directly by just returning mState, but the same error applies.

One solution would be to move the mState to protected, but as there are other classes which inherit the RandomClass, I do not think that would be a save solution.

So how would I be able to solve such an issue and resolve my errors?

For future viewers here is the working code:

class RandomClass
{
public:
  RandomClass()
  { 
    mState = 0; 
  }
  void publicFunction();
protected:
  void protectedFunction()
  {
    ++mState;
  }
private:
  int mState;

  friend class UnittestRandomClass;
};

class UnittestRandomClass : public RandomClass
{
public:
  void wrapperProtectedFunction()
  {
    protectedFunction();
  }

  void setMState(int state)
  {
    mState = state;
  }

  int getMState()
  {
    return mState;
  }
};

int main() {
  UnittestRandomClass ut;
  ut.setMState(1);
  ut.wrapperProtectedFunction();
  int res = ut.getMState();
  ASSERT_EQ(res, 2);
}

Answer 1

Your class declares a free-standing function to be friend.

Your unit test uses a member function of a class, the class is not declared friend.

You can write friend class UnitTestRandomClass;

Specifically, what you want to do, make a member function of a future derived class a friend is not provided by the standard. There is no syntax for that.