And the reason for this is because testing is inherently
incomplete. So let me re-size this a little bit, so that
I can make room for an illustration. And what I'm
going to show you here is just a reminder, that when we
test, we have a huge virtually infinite input domain, and
we have to derive from this input domain a few test
cases. By picking specific inputs in the domain, and of
course, corresponding outputs. And so what happens normally is that these
test cases represent the teeny tiny fraction of
the domain, and therefore testing is always incomplete.