Software development is rapidly changing, especially in mobile development, where adding or revamping features and technologies is crucial for customer satisfaction. To ensure functionalities work as expected, testing has become a mandatory practice for all mobile developers. There are different types of testing, including unit testing, which tests individual components with single responsibilities, focusing on narrow and well-defined scopes. Unit testing benefits include reducing costs, providing documentation, reducing code complexity, bugs, and improving design. It's an essential practice that reduces defects and allows better refactoring of code. Mobile developers can implement unit tests for iOS, Android, and Flutter apps using their respective frameworks and tools, such as XCTest, Robolectric, and flutter_test. Good unit tests should run quickly, be fully automated, and not share states with each other. Test-driven development is a technique that writes test code first before implementing the actual code, resulting in a comprehensive suite of unit tests that provide feedback on software functionality. Running unit tests on Continuous Integration (CI) pipelines, such as Bitrise, helps ensure app quality and reduces defects.