JMockit

TestNG is a testing framework inspired from JUnit and NUnit but introducing some new functionalities that make it more powerful and easier to use, such as annotations, or the possibility to run your tests in arbitrarily big thread pools with various policies available (all methods in their own thread, one thread per test class, etc.). You can test that your code is multithread safe, there is flexible test configuration, support for data-driven testing (with @DataProvider), support for parameters, powerful execution model (no more TestSuite). There is a supported by a variety of tools and plug-ins (Eclipse, IDEA, Maven, etc.), it also embeds BeanShell for further flexibility, and there is default JDK functions for runtime and logging (no dependencies), and dependent methods for application server testing. TestNG is designed to cover all categories of tests, unit, functional, end-to-end, integration, etc.

Mockito is a mocking framework that tastes really good. It lets you write beautiful tests with a clean & simple API. Mockito doesn’t give you hangover because the tests are very readable and they produce clean verification errors. Read more about features & motivations. Top 10 Java library across all libraries, not only the testing tools. In late 2013 there was an analysis made of 30.000 GitHub projects. Although Mockito reached number 9 in the main report, mockito-core and mockito-all are the same tool and therefore the factual position of Mockito is number 4, surpassing famous tools like Guava or Spring. Treat this study as an indicator of a big impact that Mockito makes every day on unit tests written in Java.