What is extreme programming (XP)?

Basic XP values

The XP methodology is based on five core values:

• Communication: Emphasis on open, frequent and direct communication among all team members and with the customer.
• Simplicity: Strive to create the simplest possible solutions that meet current requirements (YAGNI principle – You Ain’t Gonna Need It). Avoiding excessive complexity and over-engineering.
• Feedback: Continuously seek and use feedback at various levels – from unit testing, code reviews, acceptance testing, and regular customer demonstrations.
• Courage: The courage to tell the truth about progress and problems, to refactor code, to reject bad solutions and to adapt to change.
• Respect: Mutual respect between team members, respect for the customer and for the product being created.

Key XP practices

XP defines a number of specific practices that support the realization of these values. Among the most important are:

• Planning Game (Planning Game): Joint planning of releases and iterations by the team and the customer, based on user stories (user stories) and estimation of their complexity.
• Short Releases (Small Releases): Deliver working software in small, frequent releases, allowing for rapid feedback and delivery of business value.
• System Metaphor (System Metaphor): A common, simple understanding of how an entire system works that facilitates communication within a team.
• Simple Design (Simple Design): Creating the simplest possible design that meets current requirements.
• Testing: Emphasis on continuous testing at various levels: unit tests written by developers (often before code – TDD), customer-defined acceptance tests and automated tests.
• Pair Programming: Two programmers work together at the same computer – one writes code, the other observes, analyzes and suggests improvements. This increases code quality, facilitates knowledge transfer and reduces errors.
• Refactoring (Refactoring): The continuous improvement of the structure of existing code without changing its external behavior, in order to improve readability, simplicity and maintainability.
• Continuous Integration (CI): Frequent integration of code changes (several times a day) and automatic building and testing of the system.
• Collective Code Ownership: Any team member can modify any part of the system code.
• Coding Standards: Agreeing on and adhering to common standards for writing code within the team.
• Sustainable Pace: Avoiding overtime work, ensuring that the team can work efficiently over the long term.
• On-site Customer (On-site Customer): The availability of a customer representative (or product owner) to the team throughout the project to answer questions and make decisions on an ongoing basis.

Application of XP

Extreme programming is particularly effective in projects with unclear or rapidly changing requirements, where close cooperation with the client and high technical quality of code is needed. However, it requires a high degree of commitment and discipline from the entire team and openness from the client. Many XP practices (e.g. CI, TDD, Pair Programming, Refactoring) have been adopted by other agile methodologies and have become standard in modern software development.