The swipe function works when paying and invoice thru Receive Payment. NOT on a Sales receipt. So, the test you suggest would show that the card reader is working. In one of my support sessions they verified the card reader I have works testing it like you explained.  They created an investigation ticket last year after the agent witnessed the sales receipt credit card payment input screen missing all of the info after swiping via screen sharing .  Nothing changed and never received any follow up info.