To make an application more usable and attractive, we always concentrate on the logos, contents, UI, experiences, and so on, besides we also take care of the coding style. We use the latest architectures and frameworks to reduce code lines and boiler codes in order to make a robust, simple, and fast application. However, many developers forget about the testing phase. Some might not realize there's an issue until a crash report generates during application use, because they didn't adequately test during the project. Generally, some developers skip testing, as they don't want to spend some extra time on writing test cases that are not directly used in the project. This is a common mistake and results in falling quality.

Applications that randomly crash will always be disliked by the user, which is why the most successful Android apps always undergo thorough testing. In-depth testing can iron out an app's bugs, and optimize memory use, as well as allowing you to improve the condition of an app in regards to functional behavior, usabilities, and correctness. 

In this chapter, we will walk through testing and its use in both Spring and Android. This chapter covers the following topics:

• • Software testing
  • Fundamental of testing
  • Unit testing on Spring Boot
  • Creating a project
  • JUnit
  • UI testing on Android
  • Espresso