I've heard people rave about LLMs for writing tests, so I tried having Claude Code generate some tests for a bug I fixed against some autosave functionality - (every 200ms, the auto-saver should initiate a save if the last change was in the previous 200ms). Claude wrote five tests that each waited 200ms (!) adding a needless entire second to the run-time of my test suite.

I went in to fix it by mocking out time, and in the process realized that the feature was doing a time stamp comparisons when a simpler/non-error prone approach was to increment a logical clock for each change instead.

The tests I've seen Claude write vary from junior-level to flat-out-bad. Tests are often the first consumer of a new interface, and delegating them to an LLM means you don't experience the ergonomics of the thing you just wrote.