I bought a clever little tester for Christmas lights. First of all, it's a non-contact electrical tester, secondly it's a Piezo-electric generator of sorts.
It looks like a gun and has trigger. It has a place for the set plug. You plug in the set and pull the trigger. It arcs across the open shunt. Plug the set back in the mains and the set should light except for the blown lamp.
It's similar in function to a spark igniter on a gas appliance.
Dave, USradcoll 1.