[wilmoore]

Exactly...coupling is more detrimental than one would think. As your codebase gets larger and more developers on-board and features change, what should have been a simple refactor can turn into a nightmare as your test suite starts to give false negatives because you've changed the implementation or removed a now unused private function that your tests relied upon directly. Writing unit tests directly against private functions is a good way to ensure your team's velocity doesn't scale as well as it should.

Unit tests will serve you better when written to assert results rather than implementation details.