TestNG and JUnit are the two dominant Java testing frameworks. Both let you write, organize, and run tests with annotations and assertions; TestNG adds richer built-in features (groups, dependencies, data providers, parallelism, suite XML).
JUnit is the original Java unit-testing framework (JUnit 5 / Jupiter is the modern version). TestNG (Test Next Generation) was inspired by JUnit but adds capabilities aimed at larger integration/E2E suites: flexible test configuration via testng.xml, groups, method dependencies, powerful @DataProvider parameterization, built-in parallel execution, and listeners. Both integrate with Maven/Surefire, Selenium, and REST Assured. Choice often comes down to team preference and needs: JUnit 5 is excellent and extensible for unit tests; TestNG is popular for automation suites needing suite-level control. Knowing both — and their differences — is a common interview expectation.
A Selenium automation team picks TestNG for its testng.xml suite control, groups (@Test(groups='smoke')), and @DataProvider, while a library project uses JUnit 5 for clean, extensible unit tests.
In an interview: 'We already use JUnit — why might a Selenium automation team choose TestNG?'