Yeah, that only works if they follow the plan (they don't), actually write the tests first (they don't) and don't silently defer anything which doesn't have a test written as "speculative without a use case".

Or just write tests to match the buggy code after you call them out for not writing tests.

I mean, the struggle is real...

No matter how weasel-proof you make the plans they are much better weasels and just do as little as possible and "the test not written is the test which never fails." There's a certain amount of zen to them.

You write skills, prompts, and hooks to make them obey. They will obey.