Rails Maturity Models

Test-Driven Development is a continuous cycle of writing tests, developing code to make those tests pass and then refactoring.

The key thing, though, is that it's *not* about having a great test suite. That's just an awesome side-effect. The real benefit of test-driven development is in exploring the interface to your code before you've written it. From there, you wind up with less code, cleaner design and a happier, more productive development team.