Design Patterns

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Design Patterns Testability

• Principles for developing high quality software

• 26 maart 2009

• Dennis Doomen

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About Me
26 maart 2009
Dennis Doomen
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Contents

• 1830 2100
• The boring stuff
• The fun stuff
• The future
• 1930 1945
• Break

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Goal

• Michael Feathers
• I don't care how good you think your design is.
  If I can't walk in and write a test for an
  arbitrary method of yours in five minutes its not
  as good as you think it is, and whether you know
  it or not, you're paying a price for it.

26 maart 2009
Dennis Doomen
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How?

• Use coding guidelines
• Apply common design principles
• Use Design Patterns
• Socialize system design architecture
• Test Driven Development
• Refactoring

26 maart 2009
Dennis Doomen
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Coding Practices

• Avoid
• God classes
• Long methods
• Overengineering
• Micromanaging performance
• Duplication
• Bad or misleading variable names
• Use
• Coding Guidelines

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Design Principles

• Single Responsibility Principle
• Decrease Coupling, Increase Cohesion
• Open Closed Principle (open for extension, closed
  for modification)
• Liskov Substitution Pattern
• The Law Of Demeter
• Last Responsible Moment a.k.a. Reversability
• YAGNI
• Query Command Separation
• Tell, Don't Ask

26 maart 2009
Dennis Doomen
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Design Patterns

• solve common problems
• help communicate your choices
• improve object-oriented design

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Design Patterns

• Design Patterns Elements of Reusable
  Object-Oriented Software
• Eric Gamma, Richard Helm, Ralph Johnson, John
  Vlissides

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Design Patterns

• Patterns of Enterprise Application Architecture
• Martin Fowler

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Design Patterns

• Applying Domain-Driven Design and Patterns
• Jimmy Nilsson

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Test Driven Design

• is a design process, not a testing process
• Unit tests are the first users of your API
• Unit tests provide documentation
• If TDD hurts, youre doing it wrong
• Red-Green-Refactor

26 maart 2009
Dennis Doomen
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Test Principles

• Test should be
• Repeatable
• Easy to write
• Easy to understand
• Intention revealing
• Fast
• State-based versus interaction-based testing
• Mocking
• Don't mock chatty interfaces (e.g. pass
  ScreenState to View)
• Don't have more than 2-3 mocks per test
• Only mock your nearest neighbors
• Test small before testing big
• Test what you know now (and assemble the rest
  from those pieces)

26 maart 2009
Dennis Doomen
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Test Principles

• Keep your tail short
• Isolate the ugly stuff
• Keep out of the debugger jail
• Push, don't pull

26 maart 2009
Dennis Doomen
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Test Patterns

• xUnit Test Patterns, Refactoring Test Code
• Gerard Meszaros

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Demo

• 26 maart 2009

• Dennis Doomen

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Whats Next?

• Domain Driven Design
• Behavior Driven Design

26 maart 2009
Dennis Doomen
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Resources

• Jeremy D. Millerhttp//codebetter.com/blogs/jerem
  y.miller/default.aspxhttp//msdn.microsoft.com/en
  -us/magazine/cc720886.aspx
• C 3.0 Coding Guidelineshttp//blog.avivasolution
  s.nl/archive/2009/03/06/new-coding-guidelines-for-
  c-3-0.aspx
• Behavior Driven Design (Scott Belware)http//www.
  code-magazine.com/article.aspx?quickid0805061

26 maart 2009
Dennis Doomen