Start with a socket on the floor, yes the electrician can test, he will select a random socket likely to be half way, and disconnect the cables, and test which side is down to earth, so he then knows which half the fault is in, and he then splits that half in two, but it is rare for a cable to fail, rodents can cause it, but in the main it is a socket which fails.
He explained something like this in my call with him. Thanks. It makes sense. I suppose no-one cares when they know a socket on the floor is going to be hidden behind a baseboard. He also said it would be a rare case where he needed to do any chasing-out of walls.
