> If tests can do this, then so can anyone else. If I had an image loader class, I can make a test function a friend, which would allow it to call private func

> If tests can do this, then so can anyone else. If I had an image loader class, I can make a test function a friend, which would allow it to call private functions on the class. This only grants access to the test function (or test class). And there are stronger ways to hide things, like the PIMPL idiom, private headers, opaque pointers. I find it interesting we're in such different schools of thought here. > Only those that make sense to move out for separate testing would be, and only if you also wanted to expose them for others to call. There are so many things that you might want to hide from an interface, yet still test. Imagine if you took that to an extreme and only tested the public interface of a library. I'm all for trying to independently test any bit of code that fills a screen.