Your microwave may be equipped with various types of thermal fuses to monitor and control the work of the internal parts, such as Magnetron, Blower Motor, Fan Motor, etc.
Thermal fuses can be non-resettable and resettable which is also called thermal cutoff switch or thermostat. The newer models of microwaves and other appliances tend to use the resettable thermal fuses.
In your microwave, each thermal fuse controls specific internal part and monitors the temperature increase and decrease of that component. All thermal fuses, except the one that controls the fan motor, should have continuity. To test the fuse for continuity, you will need to disconnect one of its terminals and check it with multimeter.
The thermal fuse that control the magnetron can completely shut down the microwave. Its location varies depending on the type of the microwave:
In Countertop Microwave: Usually It is mounted on top of the microwave shell near the magnetron
Over the range Microwaves: Usually it is screwed directly to the magnetron
To test the thermal fuse control the magnetron, please disconnect one of the terminals of the fuse and check it for continuity with a multimeter.