[danthemanvsqz]

I don't use them on prototypes because I will throw away that code. But IMHO TDD is at it's best when your design is highly likely to change. The only protection you have against a moving target is your test suite. The requirements or our understanding of the requirements change so we change the code. In large code bases we can only be certain that the code change doesn't break anything if we have good tests. TDD is the only realistic approach to achieve 100% test coverage. You can certainly write good tests to cover your code at 100% but I've never seen it done by anyone consistently without TDD.