I once worked in a company where there was an 80% code coverage requirement. Some enterprising contractor had a script that generated a single file with its own covering test suite the size of which could be tuned to achieve 80% over the whole codebase. Mostly the code was untested.
And thanks to AI, we could generate extremely convincing reams of code whose only purpose is to be fake unit tested. Amazing. I sincerely hope I never need to use this nuclear weapon.