I built similar with a switch to change profiles in DeltaQ chargers.
It has become so useful that I made one without the switch. Testing leds was a two person job. One to push the switch.
A kid is stopping in today or tomorrow to learn how to fix led tvs. Made it for him, but it’s too nice. Let him make his own. 
Three 9v batteries, ~1k resistor to limit 30ma current, led indicator, shrink wrap.
Easy-peazy project.
