tests are an important signal of course, but the use case you describe doesn't necessarily mean you need to follow TDD. the data suggests that creating the tests after the code is just as or even more effective, and at significantly cheaper input cost.

I've been finding enforcing integrations and behavior structurally (e.g., through codegen/schemagen, e2e tests, etc) more reliable than simply instructing the models to write tests. oftentimes these tests are pretty low quality anyway, and results in its own form of tech debt.