Lid and r/h side panel off, plug out, identify white box under tub. Split circuit, meter across terminals. Somewhere between 20 and 30 ohms is acceptable.
Then remove the l/h side panel and clean out the water level chamber and transfer pipe, which will then allow enough water to enter the machine to operate the pressure switch on the end of the heater box and allow the heater to operate.
There is no test mode as far as I’m aware. If the heater is showing an acceptable reading, a no/poor heat problem on these machines is always an underfilling issue.