Help, my only vehicle isn't down electrical/alternator issue

So yesterday I was driving to work, and all of sudden the stereo starts losing power, and then my signal lights stopped working, and then my heater stopped working, then the car just died. The roadside assistance people came and jump started the car, and let it charge for about 10 minutes. We drove about 6 miles home, then went about another 6 miles to a dealership. We then went to autozone who tested the battery and alternator and said everything passed. We drove from auto zone to my college class about another 6 miles. We started having issues again just as we were getting off the freeway, and everything started losing power and the car died. We got another jumpstart, but it wasn't enough to charge it. We only made it about 1.5 miles homes. Then we charged the car from a friends car for about 20 minutes and made it most of the way home, having to stop one more time to let it charge for another 20 minutes.

My husband says its probably the alternator, my husbands friend says it sounds like a short in the electrical draining the power from the alternator/battery. Could someone please tell me what it might be and if its a short how to determine where the short is coming from so I can fix it. I cannot afford a mechanic.