The point is that tests generally only test specific inputs and circumstances. They are a heuristic, but don’t generalize to all possible states and inputs. It’s like probing a mathematical function on some points, where the results being correct on the probed points doesn’t mean the function will yield the desired result on all points of its domain. If the tests are the only measure, they become the target.

The value of a good developer is that they generalize over all possible inputs and states. That’s something current LLMs can’t be trusted to do (yet?).