My sensei does stuff like that. He does seem to tailor it to fit the individual, whatever will be the hardest on the person. I was given almost two weeks notice for my shodan (just enough time to worry and loose sleep, but not enough to actually learn anything). His step-son found out that he was testing for shodan when he was told to lead warm ups and that he was testing that day.
I kind of like the idea of watching people everyday and seeing what they do and how they act when they don't know they're under the microscope. Seems to me you'd getter a more honest representation.
That's just me though.