So basically what if when you get a question wrong in a unit test, you're presented with 2 options:

one: I got this wrong because I do not understand the concept

two: I got this wrong because I made a silly mistake

The result of one would be the traditional approach, you level down and redo the practice for it. The result of two would be you get another question of the same concept and if you do it correctly, it essentially negates your previous wrong so that you don't have to do the whole test over to "master" a topic. 

I've had this happen many times in advanced math topics where I know how to do it, I followed the procedure correctly and then simply made a little pre-algebra mistake. In such instances, I would like the opportunity to do it correctly without redoing many questions.