[ngoede]

That is not at all the assumption. The assumption is that you have some idea what you want a particular piece of code, method, or class to do and you write a test for a small piece of that and then after it passes you do that again.

At no point does TDD suggest you should know all the tests you want upfront. In fact I would expect if you know that then you don't need TDD. TDD is about learning what tests you need and what you want the object or code to look like one small piece at a time.