CT emissions: For production cars, must pass the emissions standard for the year of the make/model which since approx 1996 ( + or - ) is via a cable hook up to the vehicles recorder/diagnostic unit.
Do not know specifics, but in some cases the dyno will be used to obtain an emissions reading
The most recent change, if the Check Engine light has been re-set, the emissions testing system will invalidate the test until approx 7 days have elapsed. If the Check Engine light is on, the garage will not test the vehicle.
There are additional CT emissions web sites, 2 are
http://www.ctemissions.com/
http://www.ctemissions.com/general.html