Mockito is an open source mocking framework for Java. Mockito comes under the MIT license. The MIT license says that anybody can use the software free of charge and can use, copy, modify, merge, publish, distribute, and sell the software.

In Chapter 1, Exploring Test Doubles, we read about test doubles, spies, stubs, and mock objects. Test doubles replicate the external dependencies so that the code under test can interact with its external dependencies and allow you to isolate code from its dependencies to test them on a standalone basis. Mockito streamlines the creation and management of external dependencies and allows mock object creation, verification, stubbing, and spying on real objects. To learn more about Mockito, visit the following links: