How can I prepare to take a forensic psychiatric exam?

I am being sued for child support ( and my children ) by my ex. Mostly child support. His claim is that I am “mentally ill”. The odd part is that my own Mother agreed that I may be “bipolar”. No need to ramble on about the ridiculousness of it all, the courts are having me take the tests.
If you are a Licensed Professional Counselor, or have taken any kind of psychiatric exam, what should be my approach as the questions are asked of me.
My intent is NOT to beat the system, rather to understand the system enough to show I am indeed sane. thanks