Java unit testing involves testing individual components of software in isolation, and JUnit is a popular framework utilized for this purpose, offering features like annotations and assertions to simplify the testing process. Setting up a Java unit testing environment typically requires an integrated development environment (IDE) such as IntelliJ IDEA or Eclipse, Java JDK 8 or higher, and a build tool like Maven or Gradle to manage dependencies. JUnit provides annotations like @Test for defining test cases, and assertions like assertEquals() and assertThrows() for verifying outcomes and exceptions. The article highlights writing unit tests for arithmetic operations within a Calculator class, covering edge cases such as zero and negative numbers, and using annotations for clear reporting. Furthermore, it discusses integrating Selenium with JUnit for UI testing, leveraging LambdaTest for cross-browser testing, and adopting best practices like clear test names and isolating tests to ensure reliability. The use of AI in automating unit test generation is also suggested to enhance the Java testing workflow.