[Marc Haibeck]

A shop that advertises that they like to perform emissions oriented repairs will have an exhaust gas analyzer. Measuring the exhaust gas before the catalyst is not commonly done. They will need to weld a fitting on the pipe going into the catalyst.

For good emissions performance there is little tolerance for a misfire. The engine needs to be able to idle silky smooth. If not it should be investigated.

Note that a technician with a gas analyzer can probably give you good advice as to how the car will do on the next test based on the emissions readings, in the shop. This way you can verify that a repair is effective before going to the test.