Engine bay temperature sensor testing

Not sure if this has been written up before but anyway..
I've read in quite a few places that disconnecting the lead from the sensor and turning on the ignition will start the fan - great way of testing - but what about the sensor?

Simple!

Disconnect the lead and unscrew the sensor from its mounting. Plug the lead back in and get your or the wife/girlfriends hairdryer ready.
Start the (cold) engine and heat the sensor with the hairdryer. After a short while the sensor should heat up enough and on will come the fan. If not suspect a faulty sensor.

After testing put it all back together and job done.

Yes it's in the how to's