How do companies such as Amazon and 3DR and other drone manufactures test their drones legally in the US? For example, Amazon makes a change to one of their test drones. They take it out back of the workshop and fly it around the parking lot. Even though they did not fly it for hire or furtherance of a business they still were paying the drone engineer their engineer salary to fly the drone. Same goes for any other US based business that develops drones. How are they doing this without having an exemption?