Let's introduce various tools which help testing of java applications.
To get an idea about their usage in NetBeans, you can watch a short
.

Point to see short project info and click to visit project home page.
XTest

XTest is general test framework for Java based products tests.
XTest consists from set of utilities, templates, sample configurations and recommendations how to build integrated, flexible and easy to use test environment.
The XTest framework is planed to be base for NetBeans testing.
XTest is based on open source products like Ant, JUnit, Xalan and NetBeans.
QA

QA module provides important information related to quality of NetBeans on the Web:
- NetBeans Bug Priority Guidelines.
- Read about Q-Builds program in general.
- Check out the QA reports.
- NetBeans Quality in Graphics and Numbers.
- Stable module criteria and process document added. Read it if interested in having stable module in AutoUpdate server.
- A quick introduction to the bug-tracking system Issuezilla .
- How to report a new bug .
- Test specifications for manual testing of individual modules.
Accessibility

This module will allow you test forms in the Form Editor for accessibility issues.
This tool can also be used outside of NetBeans, through its API and as standalone application for testing your own Java applications.
JemmySupport

This module provides support for developers to create Jemmy Components for automated GUI testing.
Module also helps with I18N of tests and test components.
JUnit

JUnit framework is an opensource product that supports development of unit tests.
The module makes possible to generate skeletons for unit tests of individual classes
or whole packages, recursively including subpackages and allows to run tests from tested classes or packages.
It should be used by developers to produce unit tests for each class, join them
into test suites according to packages containing tested classes and to run these tests.
Jemmy

Jemmy is a Java
TM library that is used to create automated tests for Java GUI applications.
It contains methods to reproduce all user actions which can be performed on Swing/AWT components (i.e. button pushing, text typing, tree node expanding, ...).
It can be used with any test harness (such as XTest, for example). The programmer simply has to adopt his tests to the harness requirements.
It also can be used to create a demo for Java GUI applications. It's pretty effective for automating demo to show how an application works, showing comments during the process, and then says: Hey! Now, go ahead and play with the opened windows! This is a real application we are presenting!
Jemmy really is a NetBeansTM independent module, you can use it separately as well as together with the NetBeans IDE.