While SMT leds typically have a dot or small green line indicating their cathode, it can be hard to remember.  A quick way to test a LED is by touching the ends with a multimeter in 'Continuity Test' mode.  The multimeter generates a small voltage in order to detect a closed circuit, and this is enough to light the LED.  Although we couldn't burn out any LEDs with this Fluke, there's no guarantee your meter won't over-do the current, so we recommend doing just a quick touch, or putting a resistor in line.