I'm in transition from "writing unit tests" state to TDD.

I saw as Johannes Brodwall creates quite acceptable design from avoiding any of architecture phase before. I'll ask him soon if it was real improvisation or he had some thoughts upfront.

I also clearly understand that everyone has experience that prevents to write explicit design bad patterns.

But after participating in code retreat I hardly believe that writing test first could save us from mistakes. But I also believe that tests after code will lead to mistakes much faster.

So this night question is asking for people who is using TDD for a long time share their experience about results of design without upfront thinking. If they really practice it and get mostly suitable design. Or it's my small understanding about TDD and probably agile.