Pretty straight forward in CT...
The State of Connecticut requires emissions testing every two years on all vehicles except:
2016, 2017, 2018, 2019 model year vehicles;
Model year 1994 and older vehicles;
Vehicles with a gross vehicle weight rating of 10,001 pounds or more;
Composite Vehicles (vehicle must be titled as a composite vehicle);
Full electric-powered (non-hybrid);
Bicycles with motors attached;
Motorcycles;
Certain vehicles registered but not designed primarily for highway use;
Farm vehicles;
Diesel – Powered Type II School Buses” (under 10,000 lbs GVWR)
Vehicles with Dealer, Repairer, or Transporter Plates (only for the purpose of transportation during wholesale or auction).