LLMs are where you need the most tests.

You want them writing tests especially in critical sections, I'll push to 100% coverage. (Not all code goes there, but thing that MUST work or everything crumbles. Yeah I do it.)

There was one time I was doing the classic: Pull a bug find 2 more thing. And I just told the LLM. "100% test coverage on the thing giving me problems." it found 4 bugs, fixed them, and that functionality has been rock solid since.

100% coverage is not a normal tool. But when you need it. Man does it help.