test-driven development for developers: plain and simple

AT7 Concurrent Session 11/14/2013 2:15 PM

"Test-Driven Development for Developers:

Plain and Simple"

Presented by:

Rob Myers Agile Institute

Brought to you by:

340 Corporate Way, Suite 300, Orange Park, FL 32073 888‐268‐8770 ∙ 904‐278‐0524 ∙ [email protected] ∙ www.sqe.com

Rob Myers Agile Institute

Rob Myers is founder of the Agile Institute and a founding member of the Agile Cooperative. With twenty-seven years of professional experience on software development teams, Rob has consulted for leading companies in aerospace, government, medical, software, and financial sectors. He has been training and coaching organizations in Scrum and Extreme Programming (XP) management and development practices since 1999. Rob’s courses—including Essential Test-Driven Development and Essential Agile Principles and Practices—are a blend of enjoyable, interactive, hands-on labs plus practical dialog toward preserving sanity in the workplace. Rob performs short- and long-term coaching to encourage, solidify, and improve the team's agile practices.

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10 September 2013 © Agile Institute 2008-2013 1

TDD for Developers:

Plain & Simple

Rob Myers for

Agile Development Practices East

14 November 2013

Café


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Unit testing is soooo

DEPRESSING


TDD is fun, and provides

much more than just unit-tests!

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“The results of the case studies indicate

that the pre-release defect density of the

four products decreased between 40%

and 90% relative to similar projects that

d i d n o t u s e t h e T D D p r a c t i c e .

Subjectively, the teams experienced a

15–35% increase in initial development

time after adopting TDD.” http://research.microsoft.com/en-us/projects/esm/nagappan_tdd.pdf, Nagappan et al,

© Springer Science + Business Media, LLC 2008


=

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discipline


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TDD Demo

no magic


import junit.framework.Assert; import org.junit.Test;

public class SetTests {

@Test public void setStartsOutEmpty() {

Set mySet = new Set();

Assert.assertEquals(0, mySet.size()); }

}

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requirements & conventions




@Test

public void setStartsOutEmpty() { Set mySet = new Set();


}

Expected Actual

start simple

To Do q Empty set. q Adding an item. q Adding two different items. q Adding the same item twice.


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specification, and interface




@Test

public void setStartsOutEmpty() {



}

Will not compile. L

“Thank you, but…”


package supersets; public class Set { public int size() { throw new RuntimeException("D'oh! Not yet implemented!"); } }

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“…I want to see it fail successfully”


public class Set { public int size() {

return -1; }

}

technique: “Fake It”


package supersets;

public class Set {

public int size() {

return 0; }

}

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a. refactor away duplication


@Test public void setStartsOutEmpty() {


Assert.assertEquals(0, mySet.size());

}

public class Set { public int size() { return 0; }

}

b. triangulate


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technique: “Triangulation”


@Test public void addingItemIncreasesCount() { Set mySet = new Set(); mySet.add("One item"); Assert.assertEquals(1, mySet.size()); }

@Test

public void setStartsOutEmpty() { Set mySet = new Set();


}

technique: “Obvious Implementation”


import java.util.ArrayList; import java.util.List;

public class Set {

private List innerList = new ArrayList();

public int size() {

return innerList.size(); }

public void add(Object element) {

innerList.add(element); }

}

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maintain (refactor) the tests


Set mySet; @Before public void initializeStuffCommonToThisTestClass() { mySet = new Set(); } @Test

public void addingItemIncreasesCount() {

mySet.add("One item"); Assert.assertEquals(1, mySet.size());

}

@Test

public void setStartsOutEmpty() {


}

now for something interesting


@Test public void addingEquivalentItemTwiceAddsItOnlyOnce() { String theString = "Equivalent string"; mySet.add(theString); mySet.add(new String(theString)); Assert.assertEquals(1, mySet.size()); }

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the new behavior


public class Set { private List innerList = new ArrayList();

public int size() {

return innerList.size();

}

public void add(Object element) {

if (!innerList.contains(element)) innerList.add(element);

}

}

next?

To Do q Empty set. q Adding an item. q Adding two different items. q Adding the same item twice.


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1.  Write one unit test.

2.  Build or add to the object under test until everything compiles.

3.  Red: Watch the test fail!

4.  Green: Make all the tests pass by changing the object under test.

5.  Clean: Refactor mercilessly!

6.  Repeat.

steps


[email protected]

http://PowersOfTwo.agileInstitute.com/

@agilecoach

test-driven development for developers: plain and simple

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