Propranolol
Edit: I will elaborate on the drug.
It's a beta-blocker, obviously non-addictive, safe (for those who do not exhibit any contraindications), etc... Also used as a blood pressure medication, which is also useful considering blood pressure increases are common during states of anxiety. It is not xanax, kpins, etc... Therefore, it does not impair your mental abilities in terms of recalling information, utilizing critical thinking, etc..., and if anything, it would serve to boost memory as a result of decreased anxiety.
Many surgeons take this drug to reduce anxiety and to keep a steady hand.
I'm sorry, but your not going to forgo test taking anxiety because there is no way to condition yourself into a completely calm and relaxed state. I say this because regardless of how many practice exams you take, there will only be one that actually reflects on your grade. My strongest reduction in test taking anxiety has been during summer classes where multiple exams are taken each week, which in a sense, conditioned me.