XP and TDD - Extreme Programming and Test Driven...

Chair ofSoftware Engineering

XP and TDDExtreme Programming and Test Driven Development

Bertrand Meyer, Manuel OriolAndreas Leitner

Chair of Software EngineeringETH Zurich

October 27, 2006


Outline

Development Processes Overview

Extreme Programming

Test Driven Development



I Traditional MethodsI Waterfall modelI V modelI Spiral modelI Prototype model

I Agile MethodsI Extreme ProgrammingI Test Driven Development


Waterfall model

Figure from: Wikipedia


V model


Defect Cost

Relative cost to correct a defect

0

10

20

30

40

50

60

70

Requirements Design Code DevelopmentTesting

AcceptanceTesting

Operation

Source: Barry W. Boehm, Software Engineering Economics, Prentice Hall, 1981


Spiral model

Figure from: Ghezzi, Jazayeri, Mandrioli, Software Engineering, 2nd edition, Prentice Hall


Project Management

I Programming competence varies greatlyI 1:10 in a single group (Sackman, Erikson, Grant)

I Who introduces more bugs?I Experienced DevelopersI Beginners


Outline


Extreme Programming



XP: Motivation

I Schedule slipsI Project canceledI Systems go sourI Defect rateI Doesn’t solve actual problemI Business changesI False feature richI Staff turnover


XP: Cost of Change


XP: Rules

I The planning gameI Small ReleasesI MetaphorI Simple DesignI TestingI RefactoringI Pair programmingI Collective OwnershipI Continuous IntegrationI 40h-WeekI On-Site CustomerI Coding Standards


XP: Programming in the Wild

I Is XP like “programming in the wild”?


XP: Kinds of Testing

I Unit testingI Integration testingI System testingI Acceptance testingI Regression testing


XP: Unit testing 1/2

I ToolsI SUnit – Smaltalk (first one)I JUnit – Java (www.junit.org)I cppunit – C++I PyUnit – PythonI ...


Outline


Extreme Programming



(fromNeil McGovern)


TDD: Overview

I Evolutionary approach to developmentI Combines

I Test-first developmentI Refactoring

I Primarily a method of software designI Not just method of testing


TDD: The Process


TDD = TFD + Refactoring

I Apply test-first developmentI Refactor whenever you see fit (before next functional

modification)I Kent Beck’s rule:

I Write new business code only when a test case failsI Eliminate any duplication you find


TDD and Extreme Programming

I Easy to give in and skip some test casesI Pair-programming can helpI Writing testable code helps


TDD: Consequences

I Incremental developmentI Development environment must provide rapid response to

small changesI Components are designed highly cohesive, loosely

coupledI Developers learn to write good unit tests:

I Run fastI Run in isolationI Use data that makes test case easy to readI Each test case is step towards overall goal


TDD & Documentation

I Programmers often do not read documentationI Instead, they look for examples and play with themI Good unit tests can serve as

I ExamplesI Documentation


TDD: pros and cons

I ProsI Reduce gap between decision and feedbackI Encourage developers to write code that is easily testedI Creates a thorough test bed

I DrawbacksI Time taken away from core developmentI Some code is difficult to test


References

I Kent Beck: Agile software development: principles,patterns, and practices. Addision Wesley, 2003

I Astels: Test Driven Development: A Practical Guide,Prentice Hall, 2003

I Kent Beck: Extreme Programming Explained, AddisionWesley, 2000

I Bertrand Meyer: Practice to perfect: the quality first model,IEEE Computer, 30, 5, pages 102-103, 105-106, 1997

I Andrew Hunt: The Pragmatic Programmer: fromjourneyman to master. Addision Wesley, 2000

I Kent Beck: Extreme Programming explained. AddisionWesley, 2000

XP and TDD - Extreme Programming and Test Driven...

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