Re: Knowing you have already passed
My dojo's way of doing things is kind of similar. Students can ask Sensei if they have his permission to test. Sensei has no problem telling students to wait if he thinks they aren't ready. If he does allow them to test, this is by no means a guarantee but rather an endorsement along the lines of, "if you continue training hard and if you prepare, you will pass the test."
So...students almost always pass their tests. Only infrequently, when the student doesn't rise to the occasion, does he not pass. We don't have the kind of testing where there's usually someone who doesn't pass. Of course, there are always varying degrees of success, which influences how soon Sensei will allow you to take your next test, etc...
Testing is and should be stressful on some level, though, so I wouldn't think a guaranteed pass would be constructive.