It may seem trivial to test a common mic cable but there is more to a mic cable than 3 pins. Depending on how those pins are connected on both ends, you will either have good audio, no audio, bad audio or low level audio. A incorrectly wired cable might be acting like an antenna.
Meyer Sound has provided us with a SIM3 procedure for doing just that.
Not all of us have a SIM3 machine sitting around in which case the Rat Sound – Rat Sniffer / Sender Cable Test Kit is a good option instead.
The RAT SOUND – XLR Sniffer / Sender Cable Tester kit
I have 4 of these floating around. Since the two parts can be located away from each other, it makes it simple and fast to test things between the stage and FOH without running a long XLR cable which would be necessary with other cable testers. A set cost around $50. Well worth it.
This is a guide to what the 3 LED lights indicate:
Here is a youtube video about the Rat Sniffer / Sender with Dave Rat.