There are lots of stories about how people figured out a way to pass the "emissions" test. That link I posted has one guy confessing that he just unhooks his battery the day before he goes to get tested so the CEL goes off. I've failed a few times in my '75 Landcruiser. It gets the tailpipe sniffer, so it must be bad. I usually have to tune it up to get it pass. This past time it had 499 of the acceptable 500 Hydrocarbons or something.
The whole thing is a racket and if you noticed, we voted down a wheel tax and shortly after we got the emissions testing. $10 a pop. And if you sit in line behind the hoopties that pass, you'll want to strangle the council from all the fumes you're having to inhale in line at the testing center!
Have you ever heard that sitting in line at the drive through is bad for the environment? I always think about that when I'm sitting in line with 20 other folks, just burning the fuels and filling the planet up...kinda of makes you mad...