We all could use this tool, i can tell you from my experience, when it comes to adding a led into a circuit, although its not that a complicated job it tends to get complicated, when the tools you need to test the led, are already measuring something else, or you need to leave the desk to get them. For example if you don’t have the LED’s datasheet and usually you don’t you need to determine its color, how much current is needed to achieve that color, its voltage, its anode and cathode. So there is allot to do. Thats why the authors of this project wanted to simplify things a bit, and he assembled this project that is a standalone LED tester. The LED tester uses a 9 V battery as a power source, which provides portability.
LED Tester: [Link]