[esrauch]

In practice mutation fuzz testers are able to whitebox see where branches are in the underlying code, with a differential fuzz test under that approach its generally able to fuzz over test cases that go over all branches.

So I think under some computer science theory case for arbitrary functions its not possible, but for the actual shape of behavior in question from this library I think its realistic that a decent corpus of 'real' examples and then differential fuzzing would give you more confidence that anyone has in nearly any program's correctness here on real Earth.

[odyssey7]

Yes, there are different levels of sureness being described.

When I hear guarantee, it makes me think of correctness proofs.

Confidence is more of a practical notion for how much you trust the system for a given use case. Testing can definitely provide confidence in this scenario.