I've actually gone through and tried to refactor the tests Claude writes (when I ask it to only touch test files). I can't improve them, generally speaking. Often they're limited by architectural or code style choices in the main code. And there are minor stylistic things here or there.

But the bulk of it, is that you get absolutely top tier tests for the same level of effort as a half-assed attempt.

If you set it up with good test quality tools (mutation testing is my favorite) it goes even further - beyond what I think is actually reasonable to ask a human to test unless you're e.g. writing life and safety critical systems.