Siemon STM-8 tester is a good unit, it's what I use. And if testing a cable less than about 10 feet it will fail the "transmission test", where it looks for crosstalk between pairs. This tester will first check continuity from pin to pin, and then for split pairs. So you may pass the first portion of the test, but fail if you pinned it out wrong (or if the cable is too short to test)