TestFlight, an online service for over-the-air installation and testing of mobile applications that was purchased by Apple last year, in its most recent version 1.2 update has introduced support for testing upcoming iOS 9 features, including native Apple Watch applications with watchOS 2.
In addition, the application has been optimized with support for App Thinning, a set of Apple-provided optimization technologies designed to reduce download sizes of iOS 9 and Apple Watch apps by tailoring app delivery to the capabilities of the user’s particular device.