Oddly enough it doesn't. The secret sauce is: the robot doesn't run the tests. It digests the code and writes tests for it. So it doesn't know if they'll pass

Oddly enough it doesn't. The secret sauce is: the robot doesn't run the tests. It digests the code and writes tests for it. So it doesn't know if they'll pass or not. And sure enough, some of them don't, because the code was buggy. I've seen some awful code come out of ChatGPT, but never a bad test. Good tests are short, which makes them hard to screw up. It has a reasonable grasp on what an edge case is as well.