It takes literally 30 seconds of looking at a piece of student writing, for example, to have a pretty accurate assessment of their writing ability.
The problem is that we assume we need to test students, and not teachers.
If teaching is the problem, why are we testing students?
We don't blame bad code on the users, do we?
The second problem with your statement, is the unanswered question of who is doing the testing, and who is fiddling with the knobs. Not an easy question, but one that can't be ignored.