Stop in for a cup of coffee

A question... The PO had a small two gauge aftermarket chrome colored oil/temp hooked up under the dashboard.
Since the dash gauges were completely rebuilt a few years ago we are wiring the oil/and temp back to the dash gauges.
Is there a way to test the sending units to make sure they are working before we wire them up??
I'm sure they guy helping me has an answer, but was just curious to what you thought.