In an effort to make developing apps for an easier process, Amazon has released a suite of tools for developers to test their application through the Amazon App Store. These tools will allow a developer to push out updates to selected users to make sure the app works well in a consumer environment instead of just the test environment the app was built in. This includes testing in-app purchase APIs and stability to guarantee your app or update is rock solid before it gets pushed out to the masses.
In addition to getting valuable information about how your app performs in the real world, the testing tools allow you to easily manage who gets access to your app. Amazon handles the backbone of that process to ensure that only approved users are downloading and trying out your application. Plus, you can test the app on any Amazon platform, including Amazon's Fire Phone and Fire TV, instead of just regular Android devices accessing the App Store.
source: Amazon
