Extreme Programming Theory & XPeriences Arie van Deursen 31 October 2000 - Achtergrond CWI, SIG, Abn Amro, XP ervaring, XP conferentie - Vragen naar achtergrond bezoekers: OO ervaring? Ontwikkelaars? Projectleiders? Management? Testers? - XP = ontwikkelingsmethodiek. Kent Beck, reflecteert op eigen software ontwikkeling. - Software Ontwikkeling: wat belangrijkste “gewoontes” , “best practices”? Vb: testen, code review, UML, up fron specs - XP: zet best practices op max. - Profiteer van ontwikkelingen in techniek: OO, design pattern, relational databases, GUI, CBD http://www.cwi.nl/~arie/

Software Development Risks What are your most pressing development problems? Schedule slips Project canceled System goes sour / high defect rate Business misunderstood / changes False feature rich Staff turnover Eerst vragen: wat zijn de belangrijkste risico’s?

XP Project Characteristics Use of object technology (use of modern language) Development team size: 2 to 20 people Developers take responsibility Participating customer

XP Practices The Planning Game Small Releases Metaphor Simple design Testing Refactoring Pair programming Collective ownership Continuous integration 40-hour week On-site customer Coding standards all applied to the extreme

Self-Testing Code Every class also has a TestClass TestClass methods: set up fixture invoke code to be tested Automatically check results tear down fixture Collect test in suites; run them all. All tests must run at 100% at all times

JUnit http://www.junit.org

Test First Run all tests and get green bar; Write (failing) test before coding: if interface is unclear if implementation might be hard for every special case (if-then-else) before dealing with bug report Modify the code to turn red into green bar

Our Testing XPeriences Test / production code ratio of 1:2 Writing tests forced us to write smaller methods Test case = documentation Having many test cases helps to dare change other people’s code. Systematic reuse of each other’s tests

Refactoring Refactoring A change made Refactor: Interactive Transformation Introduce design patterns Refactoring A change made to the internal structure of software to make it easier to understand and cheaper to modify without changing its observable behavior Refactor: apply series of refactorings

Bad Smells in Code Duplicated Code Long Method Large Class Say it once! And only once! Duplicated Code Long Method Large Class Long Parameter List Divergent Change Shotgun Surgery Feature Envy Speculative Generality Inappropriate Intimacy Comments Switch Statements Data Clumps Data Class Delving into each other’s private parts Need to take some responsibility out of the cave into the centrally heated world of objects

Why Refactor? Improves the Design of Software Makes software easier to understand Refactor first to understand unfamiliar code Small refactoring -> larger ones “Wiping the dirt off a window, so you can see beyond” Helps you find bugs Helps you program faster

When should you Refactor? Three strikes and you refactor First time: just do it. Second time something similar: duplicate Third time something similar: refactor. Add feature Fix bug Review Code

Refactoring Process Modifying code involves: Test (add if necessary) Refactor to increase understanding Test Add tests for change, modify until it passes; Refactor to bring code to simplest state

Refactoring Catalog Name Summary Motivation Mechanism Examples Simple renamings up to major changes to class structure

Refactoring XPeriences Software improvement is explicit part of programming activity Possible thanks to test suites Small refactorings on a daily basis Large refactorings applied incrementally.

Simplicity XP: Have the simplest design that runs the current test suite: Code + tests communicate everything you want to communicate The system contains no duplicate code The system has the fewest possible classes The system has the fewest possible methods Achieved by constant refactoring! Vraag: eens of niet? Implicaties?

Design Through Refactoring Each change includes refactoring Each refactoring improves/repairs the design Large refactorings done by need Each refactoring = mini design-phase => Death of the big design (phase) => No separation programmer/architect

Design for Tomorrow Guess at the future. Tomorrow may never happen Learn a better way to implement a change before the time you need it Pay cost of carrying along a more complicated design Costs of unused generalizations > benefits of used generalizations

Design for Today Trust your ability to change Rely on tests Implement changes together Use modern programming technology Remove any flexibility that isn’t useful Design test by test: Repeatedly Write a test -> implies bit of design; Design & implement its code Refactor when necessary

Our Design XPeriences Designs evolve Re-design = refactoring Small refactorings done every day Major refactorings: Senior programmers involved Discussed with complete team Exploration first Implemented incrementally

Pair Programming All production code is written with two people looking at one machine, with one keyboard and one mouse. If code review is good, we do it all the time

Pair Programming XPeriences (Initial) resistance Changing pairs Discuss design, refactorings, tests Way to communicate system knowledge Improves quality (a lot) Coding is more fun, calmer, and less solitary More (> 2) productive

User Stories Collect requirements as user stories Possible to explain, test, and estimate Prioritize stories in order of business importance Development: Estimate effort for stories Highlight technical risks / consequences

Growing a System Have a running system from day 1. Integrate stories one by one Work with small iterations: Approx. 3 weeks Split (combine) stories into tasks, estimate Design, test, build, test Measure progress, learn to estimate

Planning a Release Release: every 2 - 6 months Fix date, cost and quality Determine scope: how many stories can be done following development estimates Most important user stories first Feedback / adjustment at every iteration New / modified stories Changed estimates

The Planning Game XP Planning: The Goal: Dialog between possible and desirable Set of rules to govern building respectful relationship Metaphor: Game The Goal: Maximize value of software produced by the team

Planning Game (cont.) The Strategy: The Pieces: Put the most valuable functionality into production as quickly as possible with minimal initial investment addressing risk first The Pieces: Cards containing user stories

Planning Game (cont.) The Players: The Moves: Business: decides what system must do Development: build the system The Moves: Exploration: what could system do? Commitment:decide on this release Steer: Guide actual development, adjust.

Our Planning XPeriences Planning internal product development Mimicked customer, “invented” stories Work in small iterations Always have a running system Planning customer development Made planning process “XP-like” Didn’t force customer into XP game (yet…) Learning to plan more systematically.

XP Values Communication Simplicity Feedback Courage Adopt practices that encourage talking & listening Simplicity What is the simplest thing that could possibly work? Feedback The system tests will tell you; Listen to the code! Courage Go at top speed

XP Basic Principles Rapid feedback Assume simplicity Incremental change Embracing change Quality work Teach learning Small initial investment Play to win Concrete experiments Open, honest communication Work with instincts Accepted responsibility Local adaptation Travel light Honest measurement

XP Roles Programmer -- pairing, testing, coding, designing, estimating -- courageous. Customer -- provide user stories + tests Tester -- implement functional tests Tracker -- log progress Coach -- teach to learn Consultant -- optional specialist Big Boss -- confident

Adopting XP Have motivated team Learn practices one by one Deceivingly simple tests, refactoring, pairing, planning Take sufficient time to learn Course (spread over year), mentoring But make sure you try!

Further Info K. Beck -- eXtreme Programming eXplained M. Fowler -- UML Distilled (2nd Ed.) www.c2.com/wiki www.xprogramming.com

Summary: XP Practices The Planning Game Small Releases Metaphor Simple design Testing Refactoring Pair programming Collective ownership Continuous integration 40-hour week On-site customer Coding standards all applied to the extreme