JUnit

JUnit is a unit testing framework for the Java programming language. It provides a simple API for writing repeatable tests and is widely used in Java development. The project originated in the late 1990s as part of the xUnit family, with contributions from Kent Beck and Erich Gamma. It has evolved through multiple major releases and remains the de facto standard for Java unit testing.

Core concepts in JUnit include test methods that are annotated to indicate their role. A test is typically a public void method annotated with @Test. Assertions are used to verify expected outcomes, with methods such as assertEquals, assertTrue, assertFalse, assertNull, and assertThrows. Test fixtures can be set up and torn down around tests using lifecycle annotations: in newer versions these include @BeforeEach and @AfterEach, and at the class level @BeforeAll and @AfterAll. JUnit supports grouping tests into suites and running parameterized tests, where the same test is executed with different inputs; in modern versions this is done with @ParameterizedTest and sources such as @ValueSource or @MethodSource, while older versions used @RunWith(Parameterized).

Execution and integration involve running tests from within development environments or via build tools and CI systems. JUnit tests are commonly executed by IDEs, and by build systems such as Maven and Gradle. The platform also supports backward compatibility layers to accommodate legacy test code.

JUnit's design and ecosystem have shaped Java testing practices and tooling, supporting test-driven development and continuous integration workflows. Its ongoing development includes a modular architecture that separates the test engine from the test framework, enabling both continued support for older tests and the adoption of newer programming models.