This document provides an overview of a presentation titled "Test-Driven Development for Developers: Plain and Simple" presented by Rob Myers. The presentation introduces test-driven development (TDD) and argues that it is more enjoyable and provides benefits beyond just unit testing. It demonstrates TDD techniques like writing one failing test at a time, faking functionality to get tests to compile, and refactoring code and tests. Case studies show that TDD can reduce pre-release defects by 40-90% with a 15-35% increase in initial development time.

1.
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 ∙ sqeinfo@sqe.com ∙ www.sqe.com

2. 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.

3. 9/10/13
Café
TDD for
Developers:
Plain & Simple
Rob Myers
for
Agile Development Practices
East
14 November 2013
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Unit testing
is soooo
DEPRESSING
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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
did
not
use
the
TDD
practice.
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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=
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3

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discipline
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4

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TDD Demo
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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
import junit.framework.Assert;
import org.junit.Test;
public class SetTests {
@Test
public void setStartsOutEmpty() {
Set mySet = new Set();
Assert.assertEquals(0, mySet.size());
}
}
Expected
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Actual
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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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6

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specification, and interface
import junit.framework.Assert;
import org.junit.Test;
public class SetTests {
@Test
public void setStartsOutEmpty() {
Set mySet = new Set();
Assert.assertEquals(0, mySet.size());
}
}
Will not compile. L
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“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;
}
}
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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() {
Set mySet = new Set();
Assert.assertEquals(0, mySet.size());
}
public class Set {
public int size() {
return 0;
}
}
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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();
Assert.assertEquals(0, mySet.size());
}
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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() {
Assert.assertEquals(0, mySet.size());
}
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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);
}
}
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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.
steps
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.
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Rob.Myers@agileInstitute.com
http://PowersOfTwo.agileInstitute.com/
@agilecoach
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