Like awshucks said, the spin test is just to see if you have a bent arrow or misalined head (that is where the point of the head is not on the center axis of the arrow).

I have a proper arrow straightener and an atachment to check the head alinement, but with practice just spinning the arrow on it's point, you will get to see the problems that will cause trouble. I just spin the arrow on the palm of my hand and watch for wobbles, but I could probually feel the woble more then see it (but I havbe many years of practice). Rolling the arrow on the edge of a table (feathers off the table) will help see if your arrow is bent.

In my opinion, learning to preform the spin test in the field (palm of hand) can give you a piece of mind of your arrow if you have got it caught on brush while walking with the crossbow.

Hope this helps you.