LED Keeper the only patented tool in the marketplace able to diagnose and repair most LED light sets. Easily helps remove tight bulbs from the sockets. Includes a built-in storage space for bulbs and fuses.
I always seem to have Christmas lights (all LED) breaking every year, with entire strands going out, and I finally got sick of the long and boring method of testing/fixing (swapping single bulbs known to work one at a time in and out, in and out, etc.). This is apparently the tool for the job. Note: LED only - for incandescent, you will need Light Keeper Pro.
Here's the video that shows you how to use this thing: