To paste what I just said in IRC, I'm thinking a set of questions which test a variety of Lojban topics. attitudes, name construction, lujvo construction, place tags, tanru, logical connectives, etc. and grading the testee at a particular level.
I absolutely agree that we should have some proficiency tests. In fact the more specific we get with graded levels the better, IMHO. And what I'm about to describe doesn't really qualify at all. But I thought I'd mention, since it's one related idea. Daniel Brockman once challenged me to see if I knew all of the cmavo of the form CV-- you can go through them in your head, because of the regularity: ba be bi bo bu, ca ce ci co cu, da de di do du, etc. At the time I only missed one-- I forget which one, but I remember that Daniel also had only one missing, and his was "ki". <3, selkik