The component in the pictures was taken out of a microwave which seems to be working fine except that it does not heat...
One leg of this component was connected to the capacitor and the other leg to the outer bottom metal cover (the striped side was connected to the metal cover).
From what I read, these microwave circuits usually have a diode connected between the capacitor and the magnetron and this diode breaks down often. on the other hand, I'm not sure this's a diode because it was connected to the outer cover (plus I think diodes have one stripe around the edge of them).
Normal failure mode is them going S/C, so just test it on ohms or the diode test range. However, the voltage from a meter (particularly a digital one) is most likely too low to make it conduct, but it will show if it's S/C.
However, you should be VERY, VERY aware of the high voltage and it's dangers - it's the only pretty well guaranteed fatal electric shock you will find in a home - nothing else comes close.