XP is a lightweight but disciplined approach to software development that has testing and quality at its core.
XP is based on four values: communication, simplicity, feedback, and courage.
Twelve practices comprise the rules of XP:
Onsite customer
Pair programming
Coding standards
Metaphor
Simple design
Refactoring
Testing
Continuous integration
Small releases
Planning game
Collective code ownership
Sustainable pace
XP solves three major testing and quality assurance problems:
Unit and integration bugs during system and acceptance testing
Lack of requirements from which to develop tests
Large gaps between customer expectations and delivered product