This document discusses building mobile apps and testing them using Xamarin Test Cloud. It begins by outlining challenges in mobile development like the many device types, screen sizes, and OS versions. It then introduces Xamarin Test Cloud, noting that it uses thousands of physical devices located in a warehouse to test apps across various conditions. The document proceeds to explain how to create and run tests using the Xamarin.UITest framework and IDE integrations, and view results on the Test Cloud dashboard or via email. It concludes that Xamarin Test Cloud allows for easy and fast UI testing across real devices.