Windshield problems of the 2013 Mazda CX-5

We bought our Cx-5 in April 2013. Last night when I went to get in my car I noticed a crack in the bottom middle of the windshield its about 12 inches long and curves like a hook. When I parked my Cx-5 there was no crack. When we called dealer where we bought the car he stated "a rock hit it" without even looking at the crack. My husband let him know that a rock did not hit the windshield as it was sitting in our yard. I am worried that if I take my car up to the dealership they will do the pen test and state that it was caused by a rock. There are no stars or chips on the windshield. Would like to know if there is a way to confirm this crack before they do a pen test?.