First thing to do is avoid cheap molded plug cables, the cables that come with such plugs are often the ones to develop issues. The most problem spot that develops on a cable is when the sheild/ground forms breaks in random places. I've been using the planet waves american stage series cable for 5 yrs now, bought six of them & still using the same two. These have a braided pattern on the sheild & the hot consists of twisted pair. There are other brands making such cables these days. Prior to that I had their Classic Series, it barely lasted a year of abuse.
As for a cable tester, a multimeter with continuity check mode gives off a beep when continuity is establed between the two leads, its simpler to use overall & compact ones are easier to carry around in a gig bag. Helps to check the guitar wiring is good as well before the gig starts. The one shown in a pic above is well featured but more simpler ones exist out there, like this one