Testing high power LEDs
If you want to test your high power LEDs then probably the fastest way is to tape up a couple of AA batteries, put some wires on each end and use the wires to touch the LED pads. If the LED is OK it will light up.
Make sure that you tape the batteries together with one battery’s plus (+) terminal touching the others minus (-) terminal. You don’t have to do any soldering or anything if you just make sure to tape everything up tight.
Here’s what my “LED tester” looks like
It’s cheap and it works! Make sure not to connect the batteries to the LEDs for too long, because you are over driving the LEDs and they will burn out if connected for more than just a few seconds.
Hrafnkell 
You should probably add a constant current source utilising a lm317 and a 2.5 Ohm resistor to make shure your device under test gets no more than 500 mA ufA of current. Schematics can be found easily on the internet. If you test for only a couple of seconds you don’t even need a heatsink for the lm317.
That would be true if you’re running the leds for more than 1-2 seconds. But for just testing if the polarity is correct and if they light up then 1-2 seconds at less than 3v from batteries won’t hurt them.