A colleague reported a problem that I have been able to track down and reproduce.

1.  Create a new suite (I am using NB 6 daily build 2007082012000)

2.  Add a module to the suite

3.  Create a JUnit test case in that module.  The package for the test case should be com.example.data.  

4.  For good measure, create JUnit test case in another package that does not contain data in the name, such as
com.example.tomwheeler

5.  Run the test target on your module.  The test in the package containing 'data' is neither compiled nor run.

This is caused due to a (possibly excessively broad) exclusion in the harness/common.xml, in the do-test-build target:

     <exclude name="**/data/**"/><!-- XXX for openide/util and co. -->

changing it to be something else:

     <exclude name="**/dataXXX/**"/><!-- XXX for openide/util and co. -->

eliminates the problem, as does removing the initial **/ from the name attribute.  

A workaround is obviously not to put your tests in a package containing 'data' as a directory component, but that is not
ideal because we like to have our source and test packages match.

As a side note, you cannot directly run unit tests per #108686, so you may have to get JUnit in the classpath somehow. 
I just hacked it by adding junit.jar (3.8.1) in test/ and that path to cp.extra in my nbproject/project.properties.