And that is the "COMFIRM" part of the procedure. If you pull the throttle back to confirm your identification and you do not see a change in yaw, noise etc, you have a dead engine and have correctly identified it. Go ahead and feather the same engine. If you pull the throttle back and everything goes quiet, you have mis-identified the failure; put everything back where it was and pull the other throttle. If you pull the throttle and you get a small change, and further yaw, then you have a partial failure. In this case, you might choose to push the throttle back up and use that power to get to a safe altitude before going ahead with the shut down. In some engines, such as the PW 985 round engine, this could lead to catastrophic failure with a high risk of fire, but in most flat fours or sixes, the engine will run for a few minutes at least before seizing or falling apart. He says confidently.
It might not be a simple procedure, but that is why you get paid so much to be the pic.