Here is a short prayer that you can use before an exam:
Dear God,
As I prepare to take this exam, I ask for your wisdom and guidance. Please give me the knowledge and understanding that I need to do well on this test, and help me to remember what I have studied.
Please calm my nerves and help me to stay focused, so that I may do my best. I pray for your protection over me and for your favor to be upon me as I take this exam.
I trust in your goodness and know that you are with me every step of the way.
In your holy name I pray, Amen.