I recently purchased a 2" to 2" Ferco donut to replace the hot lead and hemp on a 2" cast iron hub and connected it to a 2" schedule 40 pvc pipe. What is the best way to pressure test this so I know if it is a tite seal?

You don't need to pressure test drains since they'll never have pressure on them.

Drain a full bathtub and flush the toilet while it's draining. If it doesn't leak then, then you've probably just tested it with the maximum load that you'll ever put on it.

If you want to go further, though, fill all tubs and sinks in the house then let them go... and toss in flushing all the toilets at the same time. That'll put a bigger load on that joint than you'll ever use.