Groovy has excellent support for Unit Testing with JUnit 3.8.2 and Mocking capabilties built right in. Currently, special support doesn't exist for JUnit 4 but its easy to use so long as you are using Groovy 1.1 (currently in beta) and Java 5+ (a requirement for annotations/Junit 4.x). Here is an example.
Make sure you are using Groovy 1.1 (we used beta-2) and JUnit 4.x (we used 4.4).
Suppose we want to test the following program:
Here is what your code might look like. This example uses parameterization.
The output will look something like this: