A Mockito developer utilizes the Mockito framework, a powerful tool for creating and using mock objects in Java unit tests. They design, write, and maintain Java code that tests other code, ensuring it behaves as expected. They mock dependencies and isolate code units, allowing them to focus on the code under test. Mockito developers also simulate different scenarios, including edge cases or failures, to ensure the code can handle them. They contribute greatly to software quality assurance, helping to identify and fix bugs early in the development process and thus reducing the risk of software failure in production.