First measure the thing with a good ohmmeter. It should have close to the rated resistance between the primary (12V) wires - 5 ohm coils should be 4 to 6 ohms.
Then measure between the spark wire posts or wires. This should be a fairly high resistance, I don't have a figure to give you. Then measure from each plug post/wire to the primary wires, this should read infinity or "error" on some digital meters.
You should not power test a coil with no spark gap, it might arc inside and be damaged. If you have wires, just put a plug on each wire and tape the thread/hex parts together so the gaps are opposite and open. Then connect a 12V battery to the primary wires for a short time (a second or less) and then remove the power. The coil should spark the plugs when the power is removed. Don't hold any primary wire conductor directly or you'll get a good shock - the coil produces a fairly high voltage across the primary when the secondary sparks - only hold the insulation on the wires.
