LED / Mini Lightbulb Tester by sjroth on Instructables:

Something I love to do is to take apart old, broken electronic devices and salvage parts from them. From many of these devices I get LEDs, and testing these can be very annoying if I don’t have any 3V button cells lying around. I also occasionally use miniature lightbulbs for some projects or experiments, and they take quite some effort to test, because you need a holder. So I decided to make an LED and mini lightbulb tester.