ELM327 test bench simulator

I have a k-like ISO 9141 car that I'm developing an ELM327 project for and all of that is working fine. But doing a ton of code changes and going out to the car to test is a pain and not always possible. So I'd like to make a bench arduino module that simply simulates the vehicle and can send out any number of responses.

How do I connect to the k line interface by making my own OBD2 male plug? IE I'd like to be able to hook up a 12v source/car battery, plug in an OBD2 dongle off the shelf and connect successfully to collect simulated data.