There may be a domain where it makes a lot of sense, but I've rarely encountered it. Writing and maintaining test code takes just as much time as any other code

There may be a domain where it makes a lot of sense, but I've rarely encountered it. Writing and maintaining test code takes just as much time as any other code. You often encounter problems during the actual implementation part that challenge your preconceptions. So if you write the tests first, then you'll end up rewriting them many times. TDD also encourages you to write junk tests that provide no safety, which will then need to be maintained and fixed at every refactor. But the biggest problem is that others on the teams simply won't do it, and neither will you when a deadline looms near. TDD aspirations don't last very long in production. The one place where I think it works well is implementing a well defined protocol. If you have exact definitions for inputs and outputs, then writing the tests first can make things a lot easier. But it's rare when you have such a clean problem to solve.