DUnit automates unit testing of Delphi code. The target audience for DUnit is developers who are both writing the code to be tested and the unit tests for that code, an approach advocated by Extreme Programming. Dunit is is a Delphi port of JUnit.
This has been shipping with Delphi for a long time, and doesn't seem to have changed significantly since 2007. I think it's getting a bit stale and needs upgrading.
Excellent and unavoidable as other xUnit.
Excellent for testing source code, except user interface.