Functional tests are used to test whether several components of an app work together as expected. For example, you can create a functional test to confirm that tapping a certain button opens a new Activity. There are several functional testing frameworks for Android, but the easiest way to get started with functional testing is using the Espresso framework.
Google created Espresso to make it easier for developers to write functional tests. The library is provided through the Android support repository, so you can install it using the SDK Manager.
In order to run tests on a device, you need to define a test runner. Through the testing support library, Google provides the AndroidJUnitRunner test runner, which helps you run JUnit test classes on Android devices. The test runner will load the app APK and the test APK to a device, run all the tests, and then build the reports with the test results.
Provided you have downloaded the testing support library, this is how you...