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Chair of Software Engineering
Chair of Software Engineering
XP and TDD Extreme Programming and Test Driven Development Bertrand - - PowerPoint PPT Presentation
XP and TDD Extreme Programming and Test Driven Development Bertrand - - PowerPoint PPT Presentation
XP and TDD Extreme Programming and Test Driven Development Bertrand Meyer, Manuel Oriol Andreas Leitner Chair of Software Engineering ETH Zurich October 27, 2006 Chair of Software Engineering Outline Development Processes Overview Extreme
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Outline
Development Processes Overview Extreme Programming Test Driven Development
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Development Processes Overview
◮ Traditional Methods
◮ Waterfall model ◮ V model ◮ Spiral model ◮ Prototype model
◮ Agile Methods
◮ Extreme Programming ◮ Test Driven Development
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Chair of Software Engineering
Waterfall model
Figure from: Wikipedia
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V model
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Defect Cost
Relative cost to correct a defect
10 20 30 40 50 60 70 Requirements Design Code Development Testing Acceptance Testing Operation
Source: Barry W. Boehm, Software Engineering Economics, Prentice Hall, 1981
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Spiral model
Figure from: Ghezzi, Jazayeri, Mandrioli, Software Engineering, 2nd edition, Prentice Hall
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Project Management
◮ Programming competence varies greatly
◮ 1:10 in a single group (Sackman, Erikson, Grant)
◮ Who introduces more bugs?
◮ Experienced Developers ◮ Beginners
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Chair of Software Engineering
Outline
Development Processes Overview Extreme Programming Test Driven Development
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XP: Motivation
◮ Schedule slips ◮ Project canceled ◮ Systems go sour ◮ Defect rate ◮ Doesn’t solve actual problem ◮ Business changes ◮ False feature rich ◮ Staff turnover
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XP: Cost of Change
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XP: Rules
◮ The planning game ◮ Small Releases ◮ Metaphor ◮ Simple Design ◮ Testing ◮ Refactoring ◮ Pair programming ◮ Collective Ownership ◮ Continuous Integration ◮ 40h-Week ◮ On-Site Customer ◮ Coding Standards
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XP: Programming in the Wild
◮ Is XP like “programming in the wild”?
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XP: Kinds of Testing
◮ Unit testing ◮ Integration testing ◮ System testing ◮ Acceptance testing ◮ Regression testing
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XP: Unit testing 1/2
◮ Tools
◮ SUnit – Smaltalk (first one) ◮ JUnit – Java (www.junit.org) ◮ cppunit – C++ ◮ PyUnit – Python ◮ ...
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Chair of Software Engineering
Outline
Development Processes Overview Extreme Programming Test Driven Development
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(from Neil McGovern)
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Chair of Software Engineering
(from Neil McGovern)
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Chair of Software Engineering
(from Neil McGovern)
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TDD: Overview
◮ Evolutionary approach to development ◮ Combines
◮ Test-first development ◮ Refactoring
◮ Primarily a method of software design
◮ Not just method of testing
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TDD: The Process
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TDD = TFD + Refactoring
◮ Apply test-first development ◮ Refactor whenever you see fit (before next functional
modification)
◮ Kent Beck’s rule:
◮ Write new business code only when a test case fails ◮ Eliminate any duplication you find
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TDD and Extreme Programming
◮ Easy to give in and skip some test cases ◮ Pair-programming can help ◮ Writing testable code helps
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TDD: Consequences
◮ Incremental development ◮ Development environment must provide rapid response to
small changes
◮ Components are designed highly cohesive, loosely
coupled
◮ Developers learn to write good unit tests:
◮ Run fast ◮ Run in isolation ◮ Use data that makes test case easy to read ◮ Each test case is step towards overall goal
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TDD & Documentation
◮ Programmers often do not read documentation ◮ Instead, they look for examples and play with them ◮ Good unit tests can serve as
◮ Examples ◮ Documentation
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TDD: pros and cons
◮ Pros
◮ Reduce gap between decision and feedback ◮ Encourage developers to write code that is easily tested ◮ Creates a thorough test bed
◮ Drawbacks
◮ Time taken away from core development ◮ Some code is difficult to test
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Chair of Software Engineering