Using a friend class vs. adding accessors for unit testing in C++?

Question

Is it better to add functions that return the internal state of an object for unit testing, as opposed to making the testing class a friend? - especially, when there is no use f

Answer 1

I recommend using accessors rather than allowing access via public members or friend classes.

I don't think that using friend class actually gets you any benefits, and it has the potential to make your life a lot worse down the road. If your code is going to stay around for a long time there's a good chance that it might be used in ways that you don't anticipate. The access functions might be only used for testing now, but who knows what will happen in the future? Using accessors rather than providing direct access to variables gives you a lot more flexibility, and it has a very low cost.

The other argument is that using accessors rather than public members is a good habit. Developing good habits is an important skill as a programmer.