Mockito is a Java-based unit testing framework that simplifies automation testing by enabling the creation of mock objects to isolate the Application Under Test (AUT) from its external dependencies, improving test independence and efficiency. Often used with the JUnit framework, Mockito enhances test clarity through dependency injection and compile-time checks. It facilitates the development of test code by utilizing annotations such as @Mock, @Spy, @Captor, and @InjectMocks to specify mock behavior, thereby allowing developers to write readable and maintainable tests. Mockito's integration with JUnit 5 is simplified through extensions, eliminating the need for manual initialization and supporting parallel test execution, particularly when combined with cloud-based tools like LambdaTest for Selenium testing. This combination enables efficient cross-browser testing on numerous configurations, reducing execution time and enhancing test reliability. The tutorial illustrates the use of Mockito for creating mock objects, setting expectations, and verifying interactions, further demonstrating its application in testing scenarios such as the checkout process in eCommerce applications.