Okay, so here we have two things that are being mixed. First thing, is when you need to mark something to be used only on test, which I agree with @JB Nizet, using the guava annotation would be good.
A different thing, is to test private methods. Why should you test private methods from the outside? I mean.. You should be able to test the object by their public methods, and at the end that its behavior. At least, that we are doing and trying to teach to junior developers, that always try to test private methods (as a good practice).
