in reply to Re^2: (OT) Black- vs. white-box testing
in thread (OT) Black- vs. white-box testing

The reason why I call that white-box testing is that the private API is often explicitly designed to shine a white light on otherwise dark corners of the implementation. For instance in the regex example, you might have a flag that is available telling you which version was actually run. That allows something which should be invisible (whether you've turned on the optimization) to be tested.