You have a number of options.
1)You can test the temp display part of the system by connecting the resistor to the input connector in the rear of the instrument cluster. If you get a good reading then the fault is either the sensor or the ground connection.
However, this test requires removal of the instrument cluster which is not a trivial task.
2)The sensor is much easier to get at, and most likely the problem; if not, its days are numbered anyway. There's no need to "trash" the sensor; just desolder one end of the sensor and clip the resistor across the two wires. At worst you'll destroy a $2 part if you screw up.
But it's your call. Let me know how you decide to approach it.