Ted and Don,
Maybe the sensei knew the student's abilities, but the student didn't. That's why a test was needed
Maybe. "Needed" is such a strong word.
Certainly there are some students who, for whatever reason(s), feel as though they aren't up to par. But a 15 minute test will enlighten such a student more than weeks/months/years of training? --- how about a frank, 5 minute conversation?