Espresso is an open source framework and an instrumentation-based API, designed by Google. It is good practice to create some test cases of various scenarios of the project. It helps to find out the unexpected results or bugs of the UI, as well as the use case. It automatically syncs the actions of the test with the UI of the application. It allows you to test on both real devices and emulators. But there is a disadvantage of the use in a real device due to its high price to test various size of displays and manufacturers. So an emulator is the best solution to reduce the cost and time for testing. According to the Espresso testers, almost 99% of bugs on an Android application can be detected by this framework. The APIs of Espresso are very small, predictable, and easy to learn. You can also customize these APIs if you want. 

Let's create a project and test it with Espresso.