Air Pressure Test

I am having an air pressure test done on a bathroom that is completely finished (and has been for a year). If it fails, is there a way to find where the leak is without ripping the whole thing out?

 

I really have no experience with this. My first thought is that you can use soap bubbles on the joints that are accessible, but for connections in the wall, you may need a stethoscope to try to listen for air escaping.

Maybe you can spike some sort of mercaptan (sulfur compound) into the air tank so you could smell any leak (like in natural gas). Other than that, I don't know.