The point of unit testing, or any testing, is to make sure that the code does what it should. Public vs. private interfaces are philosophical distinctions in determining what is a "proper" unit test, and do not help in validating functionality. In order to validate that functionality testing frequently requires making changes to the class structure that would otherwise not be needed.

(Aside: I did not say private methods need to be made public to facilitate unit tests. They do, however, need to be made at least package private; this annoys me.)