To test the LEDs (all are oriented properly, the pictures help here) use your meter on Ohms, put the leads on the LEDs one way then swap the meter leads. In one direction, probably black to the flat/silver band end and red to the other, you have a good chance of lighting them. Check good ones then bad ones if the good ones light.
This verifies that they are not damaged.
BTW, in one direction you get a low resistance in the other you get a high resistance.