How do can you test the ecu if it is in functioning order?
 

There is a way to test your ecu if it is working correctly? I searched and couldn't find anything about testing the ecu itself without swaping in another ecu from another car.

This will give some advice on checking ecu while in the car. Quite informative.
https://www.rx7club.com/2nd-generation-specific-1986-1992-17/troubleshooting-your-car-ecu-340578/

That writeup is oriented more towards verifying the inputs to the ECU rather than the outputs, which is what a "bench-check" type test would do. Then again, if your ignition and fuel systems are working, those are the only outputs we're concerned about anyway, unless you're having emissions problems...