People internally make judgments about each other everyday, every moment. We gauge our world in this way. However, a student to go out with the intent to test his fellow class mate; IMO they are over stepping their boundaries. The teacher is the one with the experience and the credentials(at least she/he should have) to be putting tests upon their students. I truly feel deshi are over stepping their bounds to be testing their fellow students openly or intentionally. IMO, it goes into the category of; work on your issues before seeking out the issues in others.
For the student being "tested" by their fellow student I guess see it as a blessing that some one is "testing" you. Because, not only are YOU working on your issues, but your partner is too...all the training for you, and none for them! lol
Interesting angle that you put forward, your own level of understanding and personal opinion, and good luck with that. There is no shame or underhandedness in testing each others abilities, how else can we learn and improve? As long as it is done with the right mind, constructive and not destructive.