JUnit

JUnit is a popular unit testing framework for the Java programming language. It plays a pivotal role in test-driven development (TDD) and agile methodologies, encouraging developers to write code that is more robust, reliable, and maintainable. JUnit is part of the family of unit testing frameworks collectively known as xUnit that originated with SUnit.

JUnit provides a simple framework for writing and running tests, making it accessible even for those new to unit testing. It uses annotations (like @Test, @Before, @After, @BeforeEach, @AfterEach, @BeforeClass, @AfterClass) to indicate methods that perform tests or are to be run before/after tests.

JUnit includes a set of assertion methods to test for certain conditions; these assertions form the basis of the test validations. JUnit provides test runners which can run tests and report test results. JUnit can be easily integrated into IDEs (like Eclipse, IntelliJ IDEA) and build tools (like Maven and Gradle).

An example:

import org.junit.jupiter.api.Test;
import static org.junit.jupiter.api.Assertions.assertEquals;

public class SimpleTest {

    @Test
    public void testAddition() {
        assertEquals(4, 2 + 2, "2 + 2 should equal 4");
    }
}

SimpleTest contains a single test (testAddition) which asserts that 2 + 2 equals 4.