Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Remove black plug from High/Low gas valve solenoid

Measurement:

Measure resistance across the exposed connections of the solenoid operator (test across the two upper pins that are opposite each other) resistance should be approximately 5.2 kOhms.
Reconnect plug after test.