What exactly will your bench test comprise? Being a motion control drive, it will tuned for very fast acceleration and deceleration. Don't go cranking the pot rapidly from one extreme to the other, especially if the motor isn't clamped securely to the bench. Normally with drives like this, the motion controller takes care of ramping the speed reference. When you connect a pot directly, you become the motion controller. I'd recommend a multi-turn pot for your testing.