I've chosen to interpret TDD as "test driven design", based on the idea that systems designed to be easily unit-testable tend to also be easier to understand, m

I've chosen to interpret TDD as "test driven design", based on the idea that systems designed to be easily unit-testable tend to also be easier to understand, maintain, extend, compose, repurpose, refactor, etc. I deviate from some proponents in that I think this kind of TDD can be done while writing zero unit tests, but in practice they keep you sensitized to good design techniques. Plus the tests do occasionally catch bugs, and are otherwise a good forum to exercise your types and illustrate your code in action.