I believe it would be useful to add a MIN_TEMP and MAX_TEMP testing to the electronics box testing rig.
Testing for MIN_TEMP should proceed as follows:
- Set Marlin to heat the extruder
- Press switch to open the thermistor circuit.
- Marlin should report a MIN_TEMP error
Testing for MAX_TEMP should proceed as follows:
- Restart board
- Press switch to put a low valued resistor in parallel with the thermistor
- Marlin should report a MAX_TEMP error
Doing this test would ensure all the safeties were in place and operational.