Health testing is done at the Orthopedic Foundation for Animals.

ofa.org

You'll look for a veterinarian that does OFA exams nearest to you. The veterinarian does the exam and sends the results to the OFA. If your dog is healthy they will issue you a certificate. 

Below is an example of a certificate you will receive from the OFA if your dog is healthy. I blacked out my information but anyone that buys a puppy from me can see the full certificate for verification purposes.