Comment by ajb

This is overthinking it a bit. You mostly only need that stuff to tell you why it isn't working. If you want to know if it's up to the job, you can just measure the error rate, which just means sending a lot of data across and counting the errors. There might be some faults which only occur when the cable is in a particular position, but you can at least detect it when it happens.

The interface IC almost certainly also estimates signal quality, but it's likely hard to get that information out of it.