Car would not start

Car would not start, so took battery and had it tested thinking I needed a new battery. They charged it and it tested good. Brought it back put it back in my car car started fine. Drove down the road battery light came on the Bose sound system started flashing on and off felt like the car wanted to stall. Got back home parked it, turn the engine off. Went to started again battery drained. I had it towed into the Mazda shop. They told me I needed a new battery. $180 later driving my car home from the Mazda dealership same thing happened again. Took it back to the Mazda dealership they said I needed a complete engine wiring harness. My car is not under warranty. They told me the alternator tested good. That the wiring harness was bad as it appeared to have been wet. $1,650.00 later the dealership just called me and told me my car was ready they immediately called me back again and told me no, your car is not ready sorry now we believe it is the alternator! They said the car started up fine but shut off when they were trying to take it out of the garage. I do not think they know what it is I think they are just replacing parts or guessing at this point. Is anyone familiar with this or has anyone had a similar issue?