I would have to disagree. At some point the student is responsible for learning and performing. A teacher can't make a student learn and a teacher can't make a student perform well on any given day. I have seen people fail tests who were very capable of doing everything required for the grading. They just, for whatever reasons, didn't perform at the expected level on that day. I fail to see how this would be the instructor's fault. The instructor can provide the knowledge, training, and motivation but the student ultimately is the one who must provide an acceptable performance during the test.
You may, or may not, have noticed that I didn't say that a student's poor testing was solely
the instructor's fault. I recognize, of course, that the student bears responsibility, too, for his/her successes and failures. What proportion, exactly, you and I might not agree on, but I do agree that the student is "the one who must provide an acceptable performance during the test." Actually, this seems rather obvious to me...
I have seen quite a number of students taking a test for which they were woefully under-prepared. They were confused about terms, beginning stances (ai or gyaku hanmi), and fumbled badly through the performance of techniques. You can't hide a lack of reps; there is a quality of movement that comes only by repetition. Even if a student is having a bad day, you can tell if they put in the reps necessary to be testing. Most of the students I have seen flubbing tests did not evidence such quality of movement. In these instances, I believe the teacher, not the student, is to blame for the student's bad performance. They should not have been allowed to test until the stamp of sufficient repetitions had impressed itself upon their movements. This is the responsibility of the teacher, not the student, to judge.