I'm not sure if I agree with the idea that everything must be built out of tiny fully tested pieces. On the other hand writing a large system without testing co

I'm not sure if I agree with the idea that everything must be built out of tiny fully tested pieces. On the other hand writing a large system without testing components is insane. But most of the time I find it easier to start writing a module and then start a test and debug cycle when I'm done. I might find out half way through that the original way I wanted to solve the problem was wrong and have to rewrite most things from scratch. So it's best to write things quickly and be able to throw it away quickly. After you settle on the structure you can start to write tests to check edge cases, and verify correctness (and also to help with refactoring). I'd say this style is more like "sketch, correct, sketch some more, then polish"