Why would they even test the readings?
Here in Northern CA, they just do a scan of the computer, do the visual check of the equipment, look for smoke from the pipes and never do a sniffer test unless it is ran on adyno.
Dyno testing is only done on pre OBD vehicles.
They dyno everything here except for big trucks and motorhomes. Some years they even run a smoke test for the evaporate emission system too to check for leaks.