If you can write tests fast enough, you can specify those business rules on the fly. The ideal case is that tests always reflect current business rules. Usually that may be infeasible because of the speed at which those rules change, but I’ve had a similar experience of AI just getting tests right, and even better, getting tests verifiably right because the tests are so easy to read through myself. That makes it way easier to change tests rapidly.

This also is ignoring that ideally business logic is implemented as a combination of smaller, stabler components that can be independently unit tested.