I do strict TDD when I can, and I consider spiking out things part of the process. If I need to approach a problem that I don't know how I'd solve just yet, I c

I do strict TDD when I can, and I consider spiking out things part of the process. If I need to approach a problem that I don't know how I'd solve just yet, I create some sample code I later trash and do a lot of work in the Ruby console. Then, once I've gotten an idea of the problem, I can start writing out some pending tests that help me figure out structure, and then I'll start into the strict TDD loop of write a bit of test, watch it fail, make it pass, write more test, etc.