My view would be that if you are struggling to get useful information out of tests to that extent, then your black boxes are too big! I agree that there's noth

My view would be that if you are struggling to get useful information out of tests to that extent, then your black boxes are too big! I agree that there's nothing worse than a test that says "your stuff broke" and provides no additional information why. But there's a balance between that, and testing the internals of an implementation.