The Android testing framework is an open-source framework and one of the most WIDELY used frameworks for testing Android applications. Developers use the Android testing framework to record user interface TESTS for unit devices and Android devices.  UI (User Interface) testing ensures that your application RESPONDS to a user's actions on the device with the correct UI output. There are three SEGMENTS in the Android testing framework: 

• Application Package: This package contains the target application to be tested.
• Instrumentation Test Runner: As a Test Case Runner, it enables test cases to run/execute on the target application. Essentially, it consists of two parts: an SDK tool for creating tests, and MonkeyRunner, an API tool that ALLOWS you to write programs to control Android devices outside of Android code.
• Test Package: This package consists of two parts: test case classes (includes test methods to be performed on target application) and mock objects (include mock data used as sample input for test cases).

Most popular Android test frameworks 

• Poppy
• Detox
• Express
• Calabash
• UI Automator