Here are the noninvasive tests that where performed on me recently when I had the misfortune of being caught. Invasive tests being blood and urine samples. Firstly, I smelled to high heaven but I suppose the tests where required. Second, I was nervous and shaky as hell, as I had gotten caught. First test.
I was instructed to close my eyes and face the officer standing over me, after a little while I was told to open my eyes and focus on the flashlight he pointed at me. This was repeated several times with him having his flashlight in a different position at each. I suppose that the time it takes you to focus on the flashlights as well as the time and amount of dilation your eyes undergo is slower when you are under the influence.
I was told to stand straight, with my eyes closed and my feet together, and tilt my head back as far as I could. Kiss the sky. Then I was told to count to 30 silently, and tell the officer when I hit it. I counted to 32 on purpose, then found out I had been counting for 35, and all the while I could feel myself swaying heavily in place. Both attributes betraying my stoned psych further.
They didn't ask me many questions, as I found out that when I had foggily talked to the arresting officer I had invoked my 5th Amendment right. This apparently surprised 2 drug detectives that dropped by as they claimed I was quite young to "think of that" but that they had enough evidence against me already.