[eluser]ciscoheat[/eluser]
I know just what you mean! When you start defining how the app should work, and the tests are enforcing that afterwards... it's a great feeling.
Maybe you haven't gotten into Mock objects yet, but I think they are the best part of testing. I had a hard time to understand them in the beginning (I'll gladly explain if you like), but nowadays I mock everything to really narrow down the testing to only one class at a time. SimpleTest even has a "Partial mock" feature that enables you to replace only certain methods in a class. It's very useful, but doing that often might be a signal of a design problem.
