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

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.