I have taken two, one when I got hired and one when I joined the Bomb Squad.  If you are crazy, you fail, if you are normal, you pass.  There is no way to study or a way to "pass".  They will probably give you the standard MMPI which is about 500-1000 questions such as "I have thought about suicide", "I love my mother more than my father"  "If I was a painter I would paint flowers" ect. ect.  It is a test to see what kind of personality you have.

Advice: is to get a good night sleep, eat a good breakfast and answer with your heart, not what you think they want to hear.  Don't think. Just answer, they will all be "Yes" or "No" some may be true-false.......

Good luck, if you have made it this far you are probably almost done with your process so don't sweat the psyc. it is a small hurdle compared to the BI and the poly......

Nunyun