Extreme Programming (XP) is based on four humanistic values. These values are communication, feedback, simplicity, and courage. Testing is one incarnation of the feedback value. Testing also indirectly supports communication by providing a practical and precise way to communicate about bugs and specifications. Testing indirectly supports simplicity by enabling merciless refactoring. Testing also supports courage by removing the doubts that are often associated with changes and postponing decisions. This makes testing a very important aspect of any XP project.