I think the point is to have a unit test like for parameters in parameter_generator(n=100): assert(old_version(*parameters) == new_version(*parameters),

I think the point is to have a unit test like for parameters in parameter_generator(n=100): assert(old_version(*parameters) == new_version(*parameters), f"Versions produced different outputs on {parameters}") This lets you transform old_version with more confidence that you're not corrupting its logic.