Apple is in the late stages of testing a new ultra-thin 15-inch notebook computer that may or may not be an upcoming new addition to the MacBook Air family. MacRumors on Tuesday reports that the new ultra-thin laptop could either be a MacBook Air, which is currently offered in 11 and 13-inch sizes, or a MacBook Pro, which is currently offered in 13, 15 and 17-inch sizes. No pricing or release timing is being reported at this point, though a launch in the near term is unlikely. Apple refreshed its MacBook Pro lineup this past February and new MacBookAir models launched just this past week.