Is it just me or do whitebox unit tests really bog you down?
I do pretty much all my coding in a test-first stylee; it's the only way to code if you're snatching 20mins here and there for spare time projects. Much of the time these tests serve as scaffolding to keep me on the straight and narrow while I bootstrap up some functionality. Unfortunately after they've served this purpose they just sit there like a ball and chain round my leg slowing any future change in direction.
These days I've got into the habit of converting these tests into more stable blackbox functional tests once there's enough actual functionality to support it. Or I just delete them. Life's too short to be worrying about breaking brittle old tests.