You need to check the resistance of the sensor at several different controlled temperatures then you can plot a graph. Do it with an original sensor and a replacement sensor to see if the graph is the same. I have used inline resistors in the past to create the correct temperature reading on a gauge but under and above this it can give false readings.
I tested a spare one from an LC2 a little while ago and you basically connect a multimeter set to ohms with one lead on the tab where the single wire fits on and the other lead goes round the round part below the threaded section that goes into the coolant. If you put it in hot water the resistance should increase as the water cools. The manual says with the water temperature at 100 degrees C you should get 27.4ohms, at 80 degrees C 52.1ohms, at 60 degrees C 104 ohms and at 40 degrees C 240 ohms.