And hand-writing ten or 100 test cases might also have missed it and then we would not have known about it. Moreover, using a fixed set of test cases means that you are making certain assumptions. I would rather see two tests. The first one with a fixed set of cases, so one knows that the code at least passes this set. And a second test where you test properties against random cases. Finally, these random cases should be logged somewhere so when they cause a fail to happen, that fail can be reproduced. So. How do I log my cases?