Does my husband owe back child support?

My husband had a baby girl out of wed lock. He signed her birth certificate. She is now 3 and still doesn't look anything like him. He finally received a subpoena for child support and will be attending his first court date. Can he ask for a paternity test because he is not sure she is his? And will he owe back child support even though he was never told by court to make payments. We live in Louisiana