well if ur a wiccan or pagan i have a spell i use everytime i write a test. The spell is actually quite effective, however you do need to study before using it. It allows u to access the knowledge easier then you would stressed from the test.
as you write your name on the test say
"On this test i take today,
i will recieve no less then an A,
by the power of earth, wind fire and sea,
as i will it so mote it be."
Its a simple spell but effective. Also writing the symbol of your faith in your name works to magnify the energy being placed on yourself. Myself i place a pentacle in my name, usually in the dot in my name, like the dot in the letter "i".
Good luck on your test!