This jumps to proof assistants and barely mentions fuzzing. I've found that with a bit of guidance, Claude is pretty good at suggesting interesting properties to test and writing property tests to verify that invariants hold.

If you give Claude examples of good and bad property tests, and explain why, it gets much better than it was out of the box.

Proof assistants are the most extreme example of validation that leads you being able to trust the output (so long as the problem you intended on solving was correctly described) but fuzzing and property based testing are definitely more approachable and appropriate in most cases.