Actually, everyone's face is asymmetric. If you take a mirror and hold it so that the left half of your face is reflected, then hold it so the right half is reflected, you will see two different people. I can't really explain how to do this without pictures or drawings, so you will have to take my word for it.
But some people's faces are much more symmetrical than other people's faces. Your test will show whether this is true for a given person. The more symmetrical your facial features are, generally speaking (all other factors being equal), the better looking you are.