So that measures transfer speeds, but what about the rest of the things USB carries?
Here's an example of the data that cable testers can give you: https://m.youtube.com/watch?v=XFbJD6RE4EY
Here's an example of the data that cable testers can give you: https://m.youtube.com/watch?v=XFbJD6RE4EY
It seems like a device capable of acting as a host & device could just try to shove data down a cable and see what the max is...
Take a USB3 device, plug it in with the cable, and then go to System Profiler (Apple Menu -> About this Mac -> System Profiler). Look for the device, and check the speed. If it says 480MB/s it's a USB 2 cable, if it says 5GB/s, 10GB/s or 20GB/s then it's a USB3 cable.
I assume there's a way to do the same thing on Windows and Linux.