JUnit is an open-source testing framework for Java, designed to facilitate the creation and execution of repeatable tests. Developed by Kent Beck and Erich Gamma, it has become a standard tool in Java development, enabling developers to write and run unit tests that verify individual components of code function as intended. Key Features and Functionality: - Annotations: Simplifies test writing with annotations like `@Test`, `@BeforeEach`, and `@AfterEach` to define test methods and setup/teardown procedures. - Assertions: Provides a set of assertion methods to compare expected and actual outcomes, ensuring code behaves as expected. - Test Runners: Supports various test runners to execute tests and report results, including integration with build tools like Maven and Gradle. - Parameterized Tests: Allows running the same test with different inputs, enhancing test coverage. - Integration with IDEs: Seamlessly integrates with popular Integrated Development Environments (IDEs) such as IntelliJ IDEA and Eclipse, offering a user-friendly interface for test execution and result analysis. Primary Value and Problem Solved: JUnit addresses the need for reliable and efficient unit testing in Java applications. By automating the testing process, it helps developers identify and fix bugs early in the development cycle, leading to higher code quality and maintainability. Its integration with various tools and frameworks streamlines the development workflow, making it an essential component in modern Java development practices.