I wouldn't study or take the test high, unless you're absolutely sure you can pass that exam with flying colors.

I personally will only take a test high if it's just a lil one that's given in class every now and then that doesn't carry a lot of weight. As for finals.. nah, I'll stick to being sober while studying and taking the test... THEN after I'm finished, I will roll up a fat joint and enjoy my evening that way.