There is no such thing as a complete test suite, there will always be some possible bug that it doesn't catch.
In particular, if you put an LLM in an automated loop of "this test fails, please fix it", there is a pretty good chance that it will simply special case all of the tests, possibly in some contrived way that makes it not at all obvious when you read the code.
In particular, if you put an LLM in an automated loop of "this test fails, please fix it", there is a pretty good chance that it will simply special case all of the tests, possibly in some contrived way that makes it not at all obvious when you read the code.