Like bcat suggested, as much as possible, you need to find bugs using public interface itself. But if you want to do things like printing private variables and comparing with expected result etc(Helpful for developers to debug the issues easily), then you can make UnitTest class as friend to class to be tested. But you may need to add it under a macro like below.
class Myclass
{
#if defined(UNIT_TEST)
friend class UnitTest;
#endif
};
Enable flag UNIT_TEST only when Unit testing is required.
For other releases, you need to disable this flag.
