Comment by funcDropShadow

Your uneasiness is understandable, but often it is far simpler to check the correctness of a result than to find it in the first place. Then property-based testing really shines.

Even outside that special case it is always possible to generate just some input data and check for the absence of runtime errors or exceptions. That approach can be improved by adding assertions, pre- and postconditions to your code under test.

Additionally, there a different ways to come up with good properties, see: https://www.youtube.com/watch?v=zvRAyq5wj38