Well, with an Ethernet cable, I have one of those old LED based tester like things that had normal/rev depending on LED color.
The wiremapper is useless unless it's broken. I use long packet pings initially to help identify a bad cable.
So, there are cable testers, but I doubt they really have the ability to detect intermittents. Therefore a simple light with a current source and manually flexing the cable starting at the ends seems to work best. You can even look at the link light for an Ethernet cable.
TDR's are not very effective with long cables. I do PLAN to TDR my cable runs at some point, but I don;t have enough of them yet. Most of my Ethernet problems have been at the connector and the little tool works when you have the whole length in your hand.