If you're vibe coding, I highly recommend TDD. It makes it very easy for a coding agent to iterate on it. You gotta bonk it sometimes when it tries to delete a problematic test etc, but hallucinating a test suite along with your app really helps a lot. (I've been vibe coding a scripting language/compiler for a video game project I'm working on in this way, and it's been fascinating and mostly great.)
I get the agent to do it generally. (I realize this seems incestuous, but its fairly easy to validate the tests are sensible as you add features, because the biggest risk is regressions as the AI does something dumb later.)