[graffic]

I recommend you to take a look to the "Growing object oriented software guided by tests" book.

The first assumption you made is about TDD being only unit tests. What if TDD is not only unit tests? It could be that TDD is used in many levels, therefore when you do a more high level test, like an end to end/functional/system test, and there should be at least the idea of that system to start with. It doesn't appear suddenly.

The previous book applies TDD in that way: You get what the system has to do, prepare an idea/design of how the system has to do it and validate it through code. Of course that code is written test first.

Thus experts do not promote TDD only on units, thus "no design at all". You will find the no "BIG design upfront" though, but this is a different matter.