When I initially got my Dart running before Christmas,I ran it for a few minutes without coolant,Watched the temp gauge run into the middle of the gauge(stock cluster)

I shut it off,let it cool down and proceeded to top off the radiator with water.

Now I can drive the car around the neighborhood,and the temp gauge doesnt move one bit. Could It be the sending unit faulty? How can I test to be sure its gauge or the sender?