What Would I Need Electrical Wire Testing Hooks For?
If you remove the cap you'll have a metal dingus where you can solder a wire to. You then have a test lead which can hook onto wires, IC pins, resistor leads, you name it. Use it to make signal or power connections or as measuring leads to a DMM.  

They allow for finer work than alligator clips, which serve the same function:  

  

It's a good idea to have some test leads within reach, and to have them in different colors, so that you can tell the signals apart easily when the wiring becomes spaghetti-like; for instance use black for ground and red for your positive power supply.