JUnit

JUnit is a wildly popular unit testing framework, used primarily by developers. It is only relevant for Java code, unless you link object code from another language into a Java program, or run your test in an external process. Most of JUnit's functionality is accessed only from a Java API, but there is also a command line and a graphical interface for running tests. JUnit is a fairly simple toolset; what's powerful is that it has facilitated a surge in the practice of unit testing.

JUnit is a good choice for a unit test tool if you have Java code and developers who are willing to write unit tests. Ideally, the developers are doing "test-driven development," where the unit testing is an integral part of the development process. If you're developing in more than one language, maintaining a unit test framework for each one will take extra work. I haven't thoroughly investigated which unit test frameworks or integrated development environments support multiple languages, but it's likely that there are commercial tools that can do this.

A selling point for JUnit is that fact that the unit tests are developed in the same language as the product code, so developers can work in an environment that they're comfortable in. This selling point might not be as strong if you're wanting an independent test team to develop black-box tests. If the testers are already familiar with a different automation language, and they don't need white-box access to the product implementation, then they would likely be more productive with a tool designed for black-box testing.

JUnit is a valuable toolset to facilitate the unit testing process.