I finally get Test First! Finally.. I've been struggling with it for a while. Why? - because you don't know what it is you want to make before you start making it. Heck, even if you know the API you still don't know how it's going to actually look. Why waste your time with tests you're going to have to re-write anyway.

Well, the answer is surprisingly obvious. You have to experiment to write the code any way, right? - Often we do this in a workspace, or in a new class because we have a class name we like, or we do it in an inspector. Don't. Do it in a test case. If you do it in a test case, if it works out you can refactor it in to code+tests. Doing it this way allows you to experiment and grow. If you publish often, it also lets people see how you evolved the code. Test cases have become my birthing grounds for new code!