Damn! but doing test first programming in a pair is satisfying. My pair and I have spent the day adding a bunch of functionality to the skeleton of our new architecture and it's been fun. And really productive. I can't recommend it highly enough.
I'm refactoring some hideous code that doesn't have any tests or requirements. It's gotten to the point where after about a day, I've got 500 or so tests for about 3 modules (mostly looping over m x n configurations). There were about half a dozen different errors that the tests found for me. It's interesting to see a cascade failure, because that helps narrow down exactly what broke. The smaller failures are quite precise at finding small misunderstanding between the code and reality.
