JUnit is the standard library for writing automated tests in Java. This book contains foundational and expert knowledge for efficiently developing automated tests in Java using JUnit. It provides a compact overview of all features from JUnit 3.8.1 to JUnit 4.11 and illustrates through examples from tests of well-known open-source projects when to use these features effectively. Additionally, the author discusses open-source libraries like Mockito and FEST, which facilitate writing JUnit tests, and clarifies programming rules for writing truly "good" tests. Specifically, the book covers: - Test-driven development - Assertion libraries - Unit tests with mock objects - Writing easily understandable tests - Writing faster tests - Tests beyond the happy path - Non-functional tests. The book is rounded off with additional tips.