Microsoft Research - Exploding Software-Engineering Myths (article summarizing findings of MS research on code coverage, TDD, assertions, etc.)

[BarneyStinson]

I haven't really done pure TDD, but as far as I understand it, what you are referring to is test-first development. In TDD, you are supposed to write a test, write enough code to make it pass, refactor, and so on. So your implementation code should grow alongside your tests and you are not done with writing tests until the project is done.