what you are describing is testing invariant properties. It is telling that your two examples are math functions because those often have lots of useful invaria

what you are describing is testing invariant properties. It is telling that your two examples are math functions because those often have lots of useful invariants. A lot of time you only have weaker properties to test so you have to look for other methodologies such as using vectors of inputs/expected results or building a simpler reference implementation to test the optimized version.