@elilla Can repair: technically yes. Usually it's just a broken internal wire somewhere near (but not in) the connector, ie. the point that sees the most stress. You'll have to strip all of the insulation layers, solder the ends back together (potentially with some extra wire), and re-insulate all of it.

Can test: technically yes, but I've not seen any *affordable* ones. USB testers seem to be mostly stationary lab units, not the kind of cheap portable units that are commonly found for ethernet cables. I haven't searched especially much though.