I dont think thats a good idea. I smoked before i took the compass test and didnt do to well but my score was average but i could have done way better,
If its a serious test then I wouldn't smoke for a few days beforehand. Just make sure you are the sharpest you can be. If its just a college class placement test, then fuck it why not? My major only requires one math class and I hate math but did well on the test. I got placed into a calculas class. Instead, I opted to take the easiest math class my school offered. Why make life harder?
As long as its not for a major specific class or something that will effect your schedule later on, then yeah blaze up. Dude, no offense, but its really a simple decision. Look at the situation and then decide whether its cool for you to smoke or not. We don't know the details or what's going on in your life. I don't mean to sound like a dick, haha, sorry.