Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance

Measurement:

Measure the resistance between the threaded spindle that was previously connected to the ignition lead, and the brass connector in the end of the cap that was previously connected to the spark electrode.
Expect approximately 1 Kohm.
Also visually inspect the condition of the ignition cap.