1. TEST DRIVEN
DESIGN
AGILE NCR - APRIL 25, 2011
Jonas Auken
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2. Introduction
• Name: Jonas Auken
• Role: Agile Evangelist
• Primary goal: Excellent quality software
• Secondary goal: Happy developers
• Means: Agile practices everywhere
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3. Important questions
• How do you know if you're code is
working?
When you have tested it!
• When do you want feedback from your
code?
Now!
• When would you like to refactor?
Anytime!
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4. Agenda
• Test driven development
• The “Find my Ride” example
• Immediate feedback
• Comfortable refactoring
• Towards a better design
• Discussion: How do we get started?
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5. @Test public void canInspirePeopleToDoTDD() {
agileNCR.arrangeConference(2011);
People people = agileNCR.invitePeople();
Presenter presenter = new Presenter(“Jonas Auken”);
presenter.prepareSlides();
presenter.createExampleCode();
while (!done) {
try {
done = presenter.performPresentation(people);
} catch (QuestionRaisedException e) {
presenter.answerQuestion();
}
}
assertEquals(0.75, people.getRateInspiredToDoTDD);
}
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6. Test driven development
• Why?
• Feedback loop
• Change alarm
• Help in bug finding
• A better design
• Adding functionality by the slice
• How and when?
• Write the test first
• Mock all external objects
• Only test worker objects, not value objects
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7. Good design
• “Pretty much what you’d have expected”
• No superfluous code
• Easy to understand - easy to maintain
• Small classes, small methods
• Separation of concern - do one thing only
• Single layer of abstraction
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8. Test driven design
• The natural next step
• Avoid big design up front (BDUF)
• Design by refactoring
• Design what you need
• Mock the rest
• Small steps or large steps
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9. “Find my Ride”
• A larger example
• Web application
• A few complex issues
• Java6, JSF 2, Tomcat server, mock database
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10. This is not real
• No users telling us what they want
• No component and backend design
• No planning
• So, this is not really agile - it’s just an
example of TDD
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11. Immediate feedback
• The red-green cycle
• Test, code and refactor
• Feedback in every cycle
• Short cycle or long cycle
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12. Comfortable refactoring
• Refactoring in every cycle
• Avoid the “big refactoring in the sky”
• Refactor when the test is green
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13. Towards a better design
• Walking skeleton
• One slice of functionality
• Hardest thing first
• Knowledge is gathered
• Choices can be deferred
• Better estimates and better design
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14. How do we get started?
• Inspiration?
• Discussion?
• Questions?
• Remarks?
• Personal experiences?
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15. Books & Links
• Growing Object-Oriented Software Guided by Tests - Steve Freeman & Nat Pryce
• Test Driven Development: By Example - Kent Beck
• Extreme Programming Explained: Embrace Change - Kent Beck
• Clean Code - Robert C Martin
• Refactoring: Improving the Design of Existing Code - Martin Fowler
• 10 Ways to Improve Your Code - http://www.slideshare.net/guestebde/10-ways-to-improve-
your-code-neal-ford - Neal Ford
• SLAP - http://www.markhneedham.com/blog/2009/06/12/coding-single-level-of-
abstraction-principle - Mark Needham
• Do One Thing - http://blog.objectmentor.com/articles/2009/09/11/one-thing-extract-till-
you-drop - Robert C Martin
• Test Driven Development - http://en.wikipedia.org/wiki/Test-driven_development -
Wikipedia
• Tech & Talk - www.auken.net - Jonas Auken
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