TDD has worked well for me exactly once: porting a library from to Python to C. I had a very clear idea of what every function was supposed to do and I could w

TDD has worked well for me exactly once: porting a library from to Python to C. I had a very clear idea of what every function was supposed to do and I could write tests first. Due to the nature of the library I was able to write tests that generated lots of random inputs and check the properties of the outputs. This was a great experience --- it was very easy to change the internals without fear of breaking something. Ordinarily writing C is a bit of white-knuckle experience, but this made it quite pleasant.