The Android Test Library provides an extensive framework for testing Android apps. This library provides a set of APIs that allow you to quickly build and run test code for your apps, including JUnit 4 and functional user interface (UI) tests. You can run tests created using these APIs from the Android Studio IDE or from the command line.
The Android Test source code is stored in piper and perodically open-sourced to (http://github.com/android/android-test)