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Dror HelperSenior consultantTuesday, July 23, 2013
What’s wrong with TDD
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• Software developer & Architect > 10 years
• Senior Consultant• Agile evangelist
• Blogger – http://blog.drorhelper.com
About.Me
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What is a unit test?
A method (Code) that
tests specific functionality,
Has clear pass/fail criteria
and runs in isolation
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This is a unit test!
[TestMethod]public void CheckPassword_ValidUser_ReturnTrue()
{bool result = CheckPassword(“user”, “pass”);
Assert.IsTrue(result);}
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What about TDD?
RedWrite a failing test
GreenMake the test pass
RefactorClean duplicates and tidy up your code
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In other words:
Write new Test
Run Test
Write code
Run Tests
Refactor
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WHY DOESN’T EVERYBODY DOING IT?
If it’s so simple
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Writing tests takes time which I don’t have
orWriting tests is a waste of time
and besidesTesting is a tester’s job
Reason #1 – it got “Tests” in it
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But it takes too much time
IBM: Drivers MS: Windows MS: MSN MS: VS0%
20%
40%
60%
80%
100%
120%
140%120%
135%
115%125%
Time taken to code a feature
WithoutTDD Using TDD
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Is it a waste of time?
IBM: Drivers MS: Windows MS: MSN MS: VS0%
20%
40%
60%
80%
100%
120%
140%
61%
38%24%
9%
Using Test Driven Design
Time To Code Feature Defect density of team
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Tests costs more timeHowever Development takes less Time:• Less defects• Rarely need to invoke the debugger• Every line has a test• Overcome analysis-paralysis
So do testing waste time?
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Hope Driven Development
Can you guarantee there won’t be regression?How do you know that no stupid bugs were created?
Not testing is a decision
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Writing tests before coding is counterintuitive
How can you know what you’re going to write?
Planning for failure feels wrong
Reason #2 – Tests before code is wierd
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• Seems more logical• Don’t confuse me with new methodologies• Just as good as tests before
And Finally - no one would ever knowIt’s hard to verify were written using TDD
I’ll write the tests after
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When you write the tests after the codeYou Miss the point of TDD:
Emergent DesignOnly write the code
you need
TDD is not about the tests
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Works – but smells
funny
Development Driven Tests
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Video streamingUI
Closed architecturesLegacy code
If I can’t write tests – how can I use TDD?
Reason # 3 – Not everything is testable
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You can still test business logic
Use mocking solutions
Remember – TDD is iterative
Not everything is testable - but
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If you need tochange your code
You have toChange your tests
Reason #4 – TDD locks design
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IdeallyOnly requirement change (or defect) would cause tests to break
It means You have to know how to write robust unit tests
Tests are code too
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Requires time investmentCounter intuitiveNew skill to learnMight not work for all scenarios
TDD is:
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a safety net against regressionprevents defects during developmentEnabler of modular, testable codeOnly write the code you needTakes less time than DDT
If done correctly …
TDD is also:
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There are many excuses not to use TDD
At least try it out before deciding against it.
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Presenter contact detailsC: 972.05.7668543e: [email protected]: blog.drorhelper.comw: www.codevalue.net
