A JUnit/TestNG developer designs, writes, and maintains unit tests in Java. They use JUnit/TestNG frameworks to ensure individual units of source code (e.g., functions, methods, classes) are working correctly. These developers also create test cases and test suites, manage test data, and automate test execution. They play an essential role in the software development life cycle, particularly in Agile methodologies and Test-Driven Development (TDD). Their work helps to identify and fix bugs early, improve software quality, and accelerate the development process by reducing debugging time. They also contribute to code reviews and documentation of testing processes.