Ok guys, i thought i would put my 2 cents in. I am a service writer for a large Toyota dealership near Philly. Pre 1996 cars still get put on the rolling dyno, and get run through the full exhaust sensor testing. 1996 and up simply get an emissions computer hooked up directly to the cars on board diagnostic port. The most common reason a car will fail is due to a check engine light(should be called an emmissions light). The test can not be run if the check engine light is on. Even if the codes in the computer are reset, to temporarily shut off the light, it will not pass. There are readiness codes that are stored in the cars computer, and resetting the light resets those.
Also, even if you are emmissions exempt, your car still MUST undergo the normal safety inspection, and there is actually still a partial emissions test(basically just hooking it up to the pc to make sure everything is operational). That is why there is a charge for the emissions exemption, otherwise it would just be the cost of the sticker. Ok, sorry if i rambled, just thought i would share my knowledge on the subject.
