There's a JUnit Module for NetBeans.

*** http://netbeans.org/kb/docs/java/junit-intro.html 
*** http://netbeans.org/

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''The instructions below are outdated now''
*It's easy to integrate JavaUnit with Sun's ForteForJava.
** Add the junit.jar file to your Forte filesystem.
** Bring up the properties dialog from the context-menu of your top-level test suite.
** Select the Execution tab
** Click on the Executor property, and then click the "..." button that appears to pop up the property editor for the Executor property.
** Select External Execution in the left panel, and then click on the External Process property (the only one) in the right panel.  Click on the "..." button that appears to pop up the External Process property editor.
** Change the arguments to add the name of an appropriate test runner before the "{classname}" variable.
** Click Ok on all the dialog boxes you've opened.
** E.g. the arguments should look something like this:
** -cp {filesystems}{:}{classpath}{:}{library} junit.swingui.Test''''Runner {classname} {arguments}
**Now you can execute your test suite in the test runner by selecting the Execute option on the context menu for the test suite.
** It is also convenient to create source templates for unit tests and per-package test suites.  Just select "Save As Template..." on the context menu of a test class and select a category for the template.  Then in the "Tools|Global Options..." dialog, edit the template to a useful initial form by selecting "Open" from the template's context menu.  Now new test classes can be created very easily.