alt Hacker NewsTFineA mentions a USB cable tester. I know very little about testing or all the standards involved in USB. And I would like a way to test cables.
Is there a good reason we can't hook one (or both?) end(s) of a cable to a computer and use a program to tell what it does?
Sort of. USB-C cables have an emarker chip inside them which reports the capabilities of the cable. The USB controller on your laptop reads this chip and makes use of the info, but as of today there is no standardized way for the controller chip to pass this info up to the OS. I assume most of them don't even provide an interface at all for the OS to request it.
I vaguely recall someone from Google working on this issue for Chromebooks. I'm surprised Apple hasn't solved this since they control the OS and hardware. For now you can buy tester devices which read the emarker info and show it on a small display. There's also more advanced testers which test the actual signal integrity and error rates, but these are very expensive and made for the cable manufacturers.