2001 Chevy Camaro won't pass emission testing

What do they test for the emissions test? I'm from Pennsylvaina and all they test is the gas cap.

The smogg technitian has to tell u why its not passing. If not u must ask. Most of the time yes its the cats that r no good and wont pass. And the oxygen sensors. These are the most tipical in smog failer

Don’t go and start replacing stuff on your car just because your friend did so
be smart about things
you have a check engine light on.
Your car trying to pass along a message .
Get the code
that will help pin point the troubled area.
In the report it will include or should include the reason for failure
post code or reason here some one will help you