Re: Knowing you have already passed
My dojo test biannually. Whether you pass or not, the decision has already more or less been decided by the chief instructor (sensei) weeks in advance. When we practice, I observe that my sensei will inconspiciously observe our techniques, our kokuro (spirit) and general attitude. When the final day comes, it is more to see how we handle ourselves under pressure. If you do not make a major blunder you pass.
If you are going for higher grades, sometimes the sensei will also ask us to take over the junior grades class and he will observe you, quitely. You better know your stuff. From these activities my sensei would have decide if you are ready to move ahead.