Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Carefully remove the electrode assembly from
the combustion box door

Measurement:

Inspect the electrode for damage and good general condition.
Also measure the resistance between the tip of the spark electrode and the lead connection point.
Expect continuity / zero resistance.
Note:
Before reassembly check the integrity of all disturbed gaskets and seals and replace as necessary.