Something deeply ironic about emissions inspections in my state: my diesel VW is exempt from them. Some shops might do a cursory look to be sure you haven't deleted the particulate filter or the catalytic converter, but, really, most just make sure there is a pipe running from the exhaust manifold to the rear of the vehicle.
Last summer, I accompanied my son when he went across the state line to purchase a truck from a private seller. Said state has no inspection requirements. One of the seller's other trucks was a diesel conversion, and the exhaust was just routed up through the bonnet. Definitely no cat on that vehicle!
The emissions inspections things were important during the late 70s-80s when they were really badly done on the American cars (you could disconnect the "smog pump" and get a better running engine). This is where the diesel exemption came from - trucks had nothing much at all (and I don't think they started adding cats for quite awhile, as dirty diesel (non-low-sulfur) was very common and would kill a cat faster than curiosity).
Nowadays the real emission inspection is the computer in the car itself, continually monitoring and tracking what is going on.
A friend, who is a diesel mechanic, just went through the diesel emissions timeline with me very recently.
EGR valves -> DPFs -> DEF
I understand the necessity of these systems, but it seems like they are incredible fragile (the DPFs on VWs are prone to cracking and new ones are more than the average cat). I also understand why people do DPF deletes...
EGR and DPF on diesels are just trash and will be for the foreseeable future barring some yet unknown development in materials science. DEF, while another obnoxious consumable is pretty problem free by comparison
Last summer, I accompanied my son when he went across the state line to purchase a truck from a private seller. Said state has no inspection requirements. One of the seller's other trucks was a diesel conversion, and the exhaust was just routed up through the bonnet. Definitely no cat on that vehicle!