Nonetheless... if your state hasn't already implemented these minimum emissions tests, they ARE coming soon. Get ready.
Hmmm.... here in WA, the test is $15 and you get a free retest if you fail. Also, once you've spent $150 on diagnosis/repair at an approved specialist, you can get a waiver! So $165 worst case. Once you get the certificate, it's valid for two years and by renewing your registration early (they allow up to six months), you can milk it for three.
My 2001 Audi likes to throw "warmup catalytic converter efficiency" codes. The test is too sensitive some say. Early this year, the check engine light went off voluntarily, so I hied down to the testing station and got my three years worth for $15. Must have been running really good gas that week
I'd actually fix it, but the offending downpipes are $400 each and the official procedure is to remove the engine to replace them.
There was talk about abandoning the testing program here since so few cars fail these days. They don't test new cars nor really old ones anymore.