[thom]

I'm intrigued what level you write these tests at, because one of the most painful things to me is having to do large refactorings in a codebase with lots of little niggly unit tests, but few integration or functional tests. During a refactoring, you're constantly breaking impelementation details, and many people feel compelled to have test coverage of these details. My favourite systems are ones where use cases are explicitly modeled, or at least you have a well-defined (and tested) service layer. This is often something you'll introduce first on top of a legacy system. In systems built this way, it's far easier modify the guts, knowing you're not breaking anything with business value, but without the overhead of small unit tests that are highly coupled to implementation details.