C++ class unittests (Qt and not only)

I am pretty new to C++ unit testing and I am in the following situation: I have a class which is (of course) has public and private members. I want to test a method from private/protected section. For tests I use QtTest package but it is not strict requirement. Which is the best way of test such method?

My suggestions are:

1. Subclass it with `Test class` (multiple inheritance)
2. Add friend class (not the best way in my opinion)