Each time I was assembling a balsa wood RC plane, for instance, I would find myself into the situation where I needed to center the servo before installing it. And for this I would often have to connect all of the electronics (receiver, battery, ESC, etc) and do the designated operation from the remote control. 

   A servo tester that can be connected to a wide range of voltages up to 30V, sounded like something I really needed. Since Arduino Uno seems to have all of these peripherals ready for a wide variety of servo controls, I said to myself that it would be a very cheap and easy option. 

   If you want to build it yourself, do so by copy-pasting the code below. Check the attached schematic for reference on how to connect everything. The optional LED is only for the cases when somebody would like to incapsulate everything into an enclosure and pull the LED out on the front panel. Otherwise, the inbuilt board LED serves the same purpose. 

   Have fun and don't forget to comment and post pictures when you replicate this project, so I can rejoice with you.