OBD-II bus - emulating the car side
To emulate the CAN bus and verify the operation of devices that will attach to it, you need to emulate a portion at least of the protocol.    

There are plenty of OBD II emulators out in the market ....you could just buy one.

If you want to create your own, then I'd suggest you start here. 

This guy did a great job of both assessing current product and defining what was required to make one. 
He finally didn't achieve his goal, but he got close (high marks for that).

You could also read this ....a bit more hit-and-miss, but it may give you leads.
It's based on an Arduino, so you may find both emulator code and reader/recorder code that will help you.