I use a volt-ohm meter and set it to read the DC resistance or ohms. The plugs on the ends of a guitar cord have a positive tip and a ground sleeve or shield. I first touch the tip and ground sleeve to make sure there is no short. If there is no short, the meter should not change, if there is a short the meter will go to zero. Then I touch the two leads from the meter to both positive tips of the cord to make sure there is no break in the middle. If the cable is working OK, the meter should read zero. Then check the two outer sleeves or ground of the cable with the two leads from the meter. If there is no break in the ground or shield of the cable, the meter will go to zero.