Mockito Made Clear

If you've only ever run a few JUnit tests or injected stubs into classes to return preset values, it's time to level up your Java toolbox. Dependencies on other classes and external resources can obscure issues and make bugs hard to detect. You need to test classes in isolation to truly pinpoint your problems. And while you could write dummy classes to replace dependencies yourself, Mockito automates the process and helps you fix your code faster.
Start with the Mockito API to generate fake classes for dependencies, configure how each should respond when their methods are called, and verify that the class under test interacts with dependencies the way you'd expect. Next, build unit tests with the Mockito framework and feel confident not just that methods are called, but that they are called the correct number of times and in the correct order. Along the way, follow clear test examples based on JUnit 5 to create stubs, mocks, and spies and find the source of any problems lurking in Java classes.
Save time, write better code, and have more confidence in your Java programs with Mockito.
What You Need
In this book, we use Mockito 4, the latest version of the Mockito framework, but the concepts and the code works on versions 2 and 3. The tests are based on JUnit 5 (known as Jupiter). There are some differences in JUnit 4, but none of those affect Mockito directly. The underlying Java version is 11, but the provided tests in the GitHub repository will work successfully for any version of Java above that (including the current Long Term Support version, 17).