JUnit 5 is the latest iteration of the JUnit framework, offering significant enhancements over JUnit 4, with its architecture consisting of three main components: JUnit Platform, JUnit Jupiter, and JUnit Vintage, which facilitate running tests written in both JUnit 3 and JUnit 4. The new version requires Java 8 or higher and introduces more flexible and powerful annotations, such as @BeforeEach and @AfterEach, replacing JUnit 4's @Before and @After while ensuring better integration with modern IDEs and build tools. The tutorial underscores the advantages of JUnit 5, such as support for lambda expressions, clearer and more versatile annotation purposes, and a more extensible architecture that allows for easier migration of older tests to the new framework. It also provides detailed guidance on executing JUnit 4 tests within JUnit 5, leveraging the JUnit Vintage engine, and highlights the differences in assertions and assumptions between the two versions. This guide serves as a comprehensive resource for developers transitioning to JUnit 5, especially those involved in Selenium automation testing, offering insights into the improved testing capabilities and migration strategies.