Any test that diminishes a student's confidence and that requires the student test again for the same rank ought not to have happened in the first place. For such an unfortunate occurrence, the fault should lie primarily with the teacher, not the student, however.
...I believe that you are just restating what I have already said. Thus, the prescreen by the grading board. I will add this, Shodans and Nidans up for grading have passed the prescreening and failed the actual grading. Our gradings are performance based, principle and technique, consistency and no "uke-do".
I have been in a situation where I failed a test, and, rather than diminishing my confidence, it inspired me to spend every available night, and saturday, doing as much keiko as my body could stand. Rather than being discouraged, I was motivated to train, train, and train some more, for the month and a half or so between my failure and the re-test.
...Says great things about your character...