Honestly I've never tested one. If everything else checks good, I just throw one in there. Here are the directions on how to check though.
To test the pick-up coil, first disconnect the white and green module leads. Set the ohmmeter on the high scale and connect it between a ground and either the white or green lead. Any resistance measurement less than [COLOR=green !important][COLOR=green !important]infinity[/COLOR][/COLOR]
requires replacement of the pick-up coil.
Pick-up coil continuity is tested by connecting the ohmmeter (on low range) between the white and green leads. Normal resistance is between 500 and 1500 ohms. Move the vacuum advance arm while performing this test. This will detect any break in coil continuity. Such a condition can cause intermittent misfiring. Replace the pick-up coil if the reading is outside the specified limits