Programmation agile le cas de la programmation extrême

1. Programmation agile le cas de la programmation extrême Sylvain Giroux October 3rd, 2000

2. Plan • Quel est le problème à résoudre ? • XP: qu’est-ce ? pourquoi et quand l’appliquer ? • “X” ? • Méthodologie logicielle • Variables • Valeurs • Règles • Pratiques • Références

3. Le problème fondamental : le risque • Développement du logiciel • Échoue à livrer le logiciel, • Échoue à produire un logiciel ayant une valeur. • Glissements des échéanciers • Annulation de projets • Le système est dépassé • Quantité de défauts, bugs, etc. • Incompréhension ou changements des pratiques d’affaires • Des fonctionnalités puissantes, mais sans intérêt • Roulement de personnel

4. Méthodologie logicielle • Une méthodologie logicielle est un ensemble de règles et de pratiques utilisées pour créer des logiciels. • Une méthodologie “lourde” possède plusieurs règles, pratiques et documents. Elle requiert de la discipline et du temps pour l’appliquer correctement. • Rational Unified Process (1491 fichiers dans 159 dossiers, en 2000) • Une méthodologie “légère” a peu de règles et de partiques, qui sont faciles à appliquer.

5. Programmation extrême • Une discipline pour le développement de logiciel • pour de petites équipes (2-10 personnes) • afin de développer un logiciel • rapidement • dans un environnements où les besoins et les spécificatiosn changent rapidement.

6. Objectif de XP • Livrer le logiciel • dont on a besoin • lorsqu’on en a besoin.

7. Quand utiliser XP? • Domaines pour lesquels les besoins changent / évoluent • On ne possède pas une idée claire / définitive de ce que le système doit faire • On s’attend à des changements fréquents des fonctionnalités du système (de l’ordre de quelques mois). • Pour gérer les risques liés au projet. • Si le client a besoin d’un nouveau système à une date spécifique, le facteur de risque est grand. • Si le système présente de nouveaux défis pour l’équipe de développement, le facteur de risque est encore plus grand. • Si le système présente de nouveaux défis pour l’ensemble de l’industrie du logiciel, le facteur de risque est énorme.

8. Quand utiliser XP? • XP exige une équipe de développement étendue • Les développeurs • Les gestionnaires • Les clients • Pourquoi ? • Poser des questions, • Négocier la portée et les échéanciers, • Créer des tests fonctionnels • Demande plus que l’implication des seuls développeurs.

9. Tests • Unit Test: A test of one component of the system. Contrast with "system test." • Functional tests: Testing software based on its functional requirements. It ensures that the program physically works the way it was intended and all required menu options are present. It also ensures that the program conforms to the industry standards relevant to that environment; for example, in a Windows program pressing F1 brings up help. • Regression Test: To test revised software to see if previously working functions were impacted. • System Test: Overall testing in the lab and in the user environment. See alpha test and beta test. • Acceptance Test: The test performed by users of a new or changed system in order to approve the system and go live. Cosmetic and other small changes may still be required as a result of the test, but the system is considered stable and processing data according to requirements. • Test Case: A set of test data, test programs and expected results. • Test Scenario: A set of test cases that ensure that the business process flows are tested from end to end. • Black Box Test: Testing software based on output only without any knowledge of internal operation. Contrast with "white box test." • White Box Test: Testing software with knowledge of the internal operation. Contrast with "black box test." • http://www.pcmag.com/encyclopedia_term/0,2542,t=testing+types&i=52777,00.asp

10. Quand utiliser XP? • “Testabilité” du logiciel • Productivité • Les projets XP démontrent une plus grande productivité des développeurs lorsqu’elle est comparée à des projets similaires appartenant au même domaine corporatif.

11. Pourquoi “extrême” ? -- I • Si la revue de code est une bonne pratique, la revue de code sera réalisée en permanence (programmation par paires). • Si les tests sont importants, tous vont écrire des tests tout le temps (tests unitaires), même les clients (tests fonctionnels) • Si le design est important, le design sera partie intégrante de la pratique de tous les membres (refactorisation) • Si la simplicité est une qualité à rechercher, le système utilisera toujours le design le plus simple possible capable de supporter les fonctionnalités courantes (le plus simple qui puisse possiblement fonctionner).

12. Pourquoi “extrême” ? -- II • If architecture is important, everybody will work defining and refining the architecture all the time (metaphor) • If integration testing is important, we’ll integrate and test several times a day (continuous integration). • If short iterations are good, we’ll make the iterations really, really short –seconds and minutes and hours, not weeks and months and years (the Planning Game).

13. Four Variables • We will control four variables in our projects • Cost • Time • Quality • Scope • External forces (customers and managers) get to pick the values of 3 of the variables. • The development team gets to pick the resultant value of the 4th variable.

14. Values • XP is based on • Communication • Simplicity • Feedback • Courage.

15. Value : communication • Problems with projects can invariably be traced back to somebody not talking to somebody else about something important • A programmer doesn’t tell someone else about a critical change in the design • A programmer doesn’t ask the customer the right question, so a critical domain decision is blown • A manager doesn’t ask a programmer the right question, and project progress is misreported

16. Value : communication and XP Practices • XP practices that can’t be done without communication • Unit testing • Pair programming • Task estimation

17. Value : simplicity • What is the simplest thing that could possibly work? • Not to look toward the things you’ll need tomorrow and next week and next month • XP stance: • It is better to do a simple thing today and pay a little more tomorrow to change if it needs it, • than to do a more complicated thing today that may never be used anyway

18. Value : simplicity and XP Practices • The more you communicate, the clearer you can see exactly what needs to be done and the more you have confidence about what really doesn’t need to be done • The simpler your system is, the less you have to communicate about • Practices • Simple design • Refactoring

19. Value : Feedback at scale of minutes and days • Concrete feedback about the current state of the system • Don’t ask me, ask the system • Feedback for customers • When customers write new stories (description of features), the programmers immediately estimate them • Feedback on project progress • Watching the completion of tasks to give the whole team feedback about whether they are likely to finish everything they set out to do in a span of time

20. Value : Feedback at scale of weeks and months • The customers and testers write functional tests for all the stories (simplified use cases) implemented by the system. • The customers review the schedule every two or three weeks • to see if the team’s overall velocity matches the plan, • to adjust the plan • The system is put into production as soon as it makes sense, so the business can • begin to “feel” what the system is in action and • discover how it can best be exploited.

21. Value : Feedback and XP practices • The more feedback you have, the easier it is to communicate • Simple systems are easier to test • XP practices • The planning game • Small releases • Testing • Pair programming • Continuous integration • On-site customer

22. Value : Courage • Courage to take decisions • Radical surgery on code • Throwing code away • Starting over from scratch • Prototyping multiple design alternatives, and keep only one for “real” development

23. Last but not least Respect

24. Principles From the 4 values, a dozen or so of principles (rules) are derived to guide the development style

25. Central Principles • Main principles • Rapid feedback • time between action and feedback is critical • Assume simplicity • Incremental change • Big change made all at once just don’t work • Embracing change • Preserves the most options while solving the most pressing problem • Quality work • Nobody likes working sloppy

26. Less central principles • Teach learning • No doctrine • Small initial investment • Too many resources too early in a project is a recipe for disaster • Play to win • Playing to win vs playing not to lose • For sure we need to write reports, … but getting a working system is more important… • Concrete experiments • Every time you made a decision and you don’t test it, there is some probability that the decision is wrong.

27. Less central principles • Open, honest communication • Able to tell each other where there are problems in the code • Able to express fears and get support • Free to deliver bad news to customers and management, to deliver it early, and without being punished • Work with people’s instincts, not against them • XP is a process where following short-term self-interest (win, learn, be in control, good work…) also serves long-term team interest • Accepted responsibility • Not telling people what to do • Does not mean that you always do exactly what you feel like doing

28. Less central principles • Local adaptation • Adapt XP principles and practices to local conditions • Travel light • You can’t expect to carry a lot of baggage and move fast • Be prepared to change direction • Artifacts • Few • Simple • Valuable • Honest measurement • This will take 14.176 hours (???)

29. Back to basics • There are 4 activities to support • Coding • Testing • Listening • Designing

30. XP Practices • What is a practice? the usual way of doing something • Aim of practices in XP: • Structure the 4 activities • In XP, there are 12 practices

31. 12 Practices • The Planning Game • Small Releases. • Metaphor. • Simple Design. • Testing. • Refactoring. • Pair Programming. • Collective Ownership. • Continuous Integration. • 40-hour Week. • On-site Customer. • Coding Standard.

32. Practice: The Planning Game • Determine • what will be accomplished by the due date, • determining what to do next • The XP "customer“ • define the business value of desired features • The programmer • provides cost estimates • The XP "customer“ • choose • what needs to be done • what needs to be deferred

33. Practice: Small releases XP teams • put a simple system into production early, • update it frequently on a very short cycle

34. Practice: Metaphor XP teams use • common "system of names" and a • common system description • that guide development and communication • We don’t literally mean “the system is…” • Give everyone a coherent story within which to work • Help everyone on the project understand the basic elements and their relationships • "this program works like a hive of bees, going out for pollen and bringing it back to the hive" as a description for an agent-based information retrieval system

35. Practice: Simple design • A program built with XP should be the SIMPLEST program that meets the current requirements. • There is not much building "for the future".

36. Practice: Testing • XP teams focus on validation of the software at all times. • Programmers develop software by writing tests first, then software that fulfills the requirements reflected in the tests. • Customers provide acceptance tests that enable them to be certain that the features they need are provided.

37. Practice: Refactoring • XP teams improve the design of the system throughout the entire development • removal of duplication (a sure sign of poor design), • on increasing the "cohesion" of the code, while lowering the "coupling". • High cohesion and low coupling have been recognized as the hallmarks of well-designed code for at least thirty years • This is done by keeping the software clean • without duplication • with high communication • simple • yet complete

38. Practice: Pair Programming • XP programmers write all production code in pairs, • two programmers working together at one machine

39. Practice: Collective ownership • All the code belongs to all the programmers • This lets the team go at full speed, because when something needs changing, it can be changed without delay

40. Practice: Continuous integration • XP teams integrate and build the software system multiple times per day • This keeps all the programmers on the same page, and enables very rapid progress • integrating more frequently tends to eliminate integration problems that plague teams who integrate less often

41. Practice: 40-hour week (sustainable pace) • Tired programmers make more mistakes. • XP teams do not work excessive overtime, • keeping themselves fresh, healthy, and effective • This means that they work overtime when it is effective, and that they normally work in such a way as to maximize productivity week in and week out.

42. Practice: On-site customer • An XP project is steered by a dedicated individual who is empowered to • determine requirements, • set priorities, • answer questions as the programmers have them

43. Practice: Coding standards • to work effectively in pairs, • to share ownership of all the code, • all the programmers need to write the code in the same way • with rules that make sure the code communicates clearly Software, naming, language, {}…

44. XP map A spike solution is a very simple program to explore potential solutions

45. References • Kent beck, Extreme Programming Explained: Embrace Change, Addison Wesley, 2000 • Martin Fowler, Refactoring : Improving the Design of Existing Code, Addison-Wesley, 1999 • http://www.xprogramming.com • http://www.xprogramming.com/xpmag/index.htm • http://www.xprogramming.com/Practices/xpractices.htm • http://www.extremeprogramming.org/