That's a whole discussion on its own. Tests do not have to guarantee that the behavior is correct for all possible inputs. If testing all possible inputs is ea

That's a whole discussion on its own. Tests do not have to guarantee that the behavior is correct for all possible inputs. If testing all possible inputs is easy, do it. Otherwise, you write the tests which you think are most likely to catch errors. Try to exercise different code paths to catch errors in different parts of the code. Try to use different logic in your test from the logic in the code under test.