This is my experience as well. If you want it to write good tests, you have to take a much more involved approach of first making it establish what needs testing in each module, writing each test one at a time, and making it prove that it can break the test by modifying the source code to introduce a bug, modify the test to be appropriate, rinse and repeat. I haven't done this much because it's very expensive in terms of time and premium tokens...right now, I just write most tests myself so at least I have faith in the verification suite.

claude is like an intern, someone has to code review and approve before final delivery imho