There's a new Xamarin book on sale, written by Jim Bennett, Microsoft MVP and Cloud Developer Advocate at Microsoft
Among other topics, the author talks about MVVM, Xamarin.Android, Xamarin.iOS, testing with UI Test and physical device, as well as using App Center for app testing and monitoring. There's also a discussion about beta distribution and publishing.
It is possible to download the first and sixth chapters from the website.
Use the code mlbennett2lt for a 50% discount (available today only). In case it has already expired, you can instead use the code xamarininaction to get a 42% discount.
Physical and digital versions available.