Criminal Defense – What Happens During A DUI Stop? In a DUI case, after they pull you over, the police will often have you do roadside tests, which are referred to a as field sobriety tests (FSTs). One is the Horizontal Gaze Nystagmus (HGN) test. In this test the police officer will stand in front of you and move his finger or a pen back and forth in front of your face and have you follow it with your eyes without moving your head. If you do this test and your eyes show Nystagmus, which is involuntary jerking of the eye, this is an indication of being under the influence of alcohol. Another test they will often have you do is the Walk and Turn test. This is a test in which you walk a straight line, heel to toe, nine steps forward, turn around and walk nine steps back.