A definitive test that measures the amount of moisture released from the concrete requires a calcium chloride kit or a relative humidity meter.
How to test basement floor for moisture.
Seal around the edges and leave it for several days.
If you get moisture on the exposed surface then the problem is condensation.
If you find moisture on the bottom you have moisture in the slab.
Look for condensation on the underside of the plastic sheet or a visible darkening of the slab below the plastic that is damp to the touch.
Moisture on the top more common in a basement is a sign of condensation from high humidity in the room.
Using duct tape fasten pieces of heavy plastic or aluminum foil about 20 inches square to several spots on the floor.
Check the squares every few days.