1. TDD FOR THE WIN
Basics to Test Driven Development
May 2014 Minh Ngoc Dang

2. Senior Developer at ThoughtWorks
ThoughtWorks University Trainer
Minh Ngoc Dang

3. TESTING

4. WHY TESTING?
Lots of reasons! Here are a select few
Verify functionality of
application
Catch bugs and prevent them from
coming back
Serve as documentation for
maintainability purposes

5. BUT WHAT ABOUT…?
? How do we make sure we have full test coverage?
? How can we be confident all cases are covered?
? How can we prevent bugs from happening?

6. TDD!

7. TEST DRIVEN DEVELOPMENT!

8. BUT WAIT…WHAT IS IT?

9. BUT WAIT…WHAT IS IT?

10. TEST DRIVING MEANS
Writing tests before writing code
Write the minimum amount of code
necessary to make tests pass
Rinse and repeat

11. TESTS FIRST?! BUT
WHY?

12. WHY TDD?
Back to previously posed questions
Test
Coverage?
Cases Covered? Bug Prevention?

13. TEST COVERAGE
Tests written before code

14. TEST COVERAGE
Tests written before code
Ensure all code covered by tests

15. TEST COVERAGE
Tests written before code
Ensure all code covered by tests
High test coverage

16. WHY TDD?
Back to previously posed questions
Test
Coverage?
Cases Covered? Bug Prevention?

17. TEST CASES
Test cases reflect exactly what code
does

18. TEST CASES
Test cases reflect exactly what code
does
Visible list of functionality

19. TEST CASES
Test cases reflect exactly what code
does
Visible list of functionality
Easy to see which
cases are missing

20. WHY TDD?
Back to previously posed questions
Test
Coverage?
Cases Covered? Bug Prevention?

21. BUG PREVENTION
Mental shift in thinking up test case
before code

22. BUG PREVENTION
Mental shift in thinking up test case
before code
Encourage edge case testing

23. BUG PREVENTION
Mental shift in thinking up test case
before code
Encourage edge case testing
Help prevent bugs in
edge cases

24. WHY TDD?
Back to previously posed questions
Test
Coverage?
Cases Covered? Bug Prevention?

25. AND THAT’S NOT ALL!

26. TIME SAVER
Ease in debugging
Confidence in refactoring

27. DRIVING DESIGN
Help define usage – How should the
code be used?
Only write necessary code – YAGNI!

28. SO HOW CAN I TDD?

29. RED – GREEN - REFACTOR
New Test New Test New Test
Red
GreenRefactor
Red
GreenRefactor
Red
GreenRefactor

30. EXAMPLE
You are given strings of different lengths. If
the number of vowels are more than 30%
of the string length then insert ‘mommy’ for
each continuous set of vowels.
 his → hmommys
 hear → hmommyr
✗ hear → hmommymommyr

31. TEST CASES
“” → “” // empty string
“str” → “str” // no vowels
“a” → “mommy” // single vowel
“blah” → “blah” // < 30% length
“bla” → “blmommy” // > 30% length
“blaa” → “blmommy” // continuous vowels
“blaaha” → “blmommyhmommy”
// multi sets of vowels
“blA” → “blmommy” // capital letters
Null → raise exception // null checks

32. TEST
import org.junit.Test;
import static org.junit.Assert.assertEquals;
public class MommifierTest {
@Test
public void shouldNotMommifyEmptyString() {
String word = "";
Mommifier mommifier = new Mommifier();
String mommifiedWord = mommifier.mommify(word);
assertEquals("", mommifiedWord);
}
}

33. SOURCE
public class Mommifier {
public String mommify(String word) {
return null;
}
}

34. TEST
import org.junit.Test;
import static org.junit.Assert.assertEquals;
public class MommifierTest {
@Test
public void shouldNotMommifyEmptyString() {
String word = "";
Mommifier mommifier = new Mommifier();
String mommifiedWord = mommifier.mommify(word);
assertEquals("", mommifiedWord);
}
}

35. SOURCE
public class Mommifier {
public String mommify(String word) {
return "";
}
}

36. TEST
import org.junit.Test;
import static org.junit.Assert.assertEquals;
public class MommifierTest {
@Test
public void shouldNotMommifyEmptyString() {
String word = "";
Mommifier mommifier = new Mommifier();
String mommifiedWord = mommifier.mommify(word);
assertEquals("", mommifiedWord);
}
}

37. TEST
import org.junit.Test;
import static org.junit.Assert.assertEquals;
public class MommifierTest {
@Test
public void shouldNotMommifyEmptyString() {...}
@Test
public void shouldNotMommifyWordsWithNoVowels() {
String word = "str";
Mommifier mommifier = new Mommifier();
String mommifiedWord = mommifier.mommify(word);
assertEquals("str", mommifiedWord);
}
}

38. TEST
import org.junit.Test;
import static org.junit.Assert.assertEquals;
public class MommifierTest {
@Test
public void shouldNotMommifyEmptyString() {...}
@Test
public void shouldNotMommifyWordsWithNoVowels() {
String word = "str";
Mommifier mommifier = new Mommifier();
String mommifiedWord = mommifier.mommify(word);
assertEquals("str", mommifiedWord);
}
}

39. SOURCE
public class Mommifier {
public String mommify(String word) {
return word;
}
}

40. TEST
import org.junit.Test;
import static org.junit.Assert.assertEquals;
public class MommifierTest {
@Test
public void shouldNotMommifyEmptyString() {...}
@Test
public void shouldNotMommifyWordsWithNoVowels() {
String word = "str";
Mommifier mommifier = new Mommifier();
String mommifiedWord = mommifier.mommify(word);
assertEquals("str", mommifiedWord);
}
}

41. TEST
import org.junit.Test;
import static org.junit.Assert.assertEquals;
public class MommifierTest {
@Test
public void shouldNotMommifyEmptyString() {...}
@Test
public void shouldNotMommifyWordsWithNoVowels() {...}
@Test
public void shouldMommifyVowel() {
String word = "a";
Mommifier mommifier = new Mommifier();
String mommifiedWord = mommifier.mommify(word);
assertEquals("mommy", mommifiedWord);
}
}

42. TEST
import org.junit.Test;
import static org.junit.Assert.assertEquals;
public class MommifierTest {
@Test
public void shouldNotMommifyEmptyString() {...}
@Test
public void shouldNotMommifyWordsWithNoVowels() {...}
@Test
public void shouldMommifyVowel() {
String word = "a";
Mommifier mommifier = new Mommifier();
String mommifiedWord = mommifier.mommify(word);
assertEquals("mommy", mommifiedWord);
}
}

43. SOURCE
public class Mommifier {
public String mommify(String word) {
for (char character : word.toCharArray()) {
if (character == 'a'
|| character == 'e'
|| character == 'i'
|| character == 'o'
|| character == 'u'){
return "mommy";
}
}
return word;
}
}

44. TEST
import org.junit.Test;
import static org.junit.Assert.assertEquals;
public class MommifierTest {
@Test
public void shouldNotMommifyEmptyString() {...}
@Test
public void shouldNotMommifyWordsWithNoVowels() {...}
@Test
public void shouldMommifyVowel() {
String word = "a";
Mommifier mommifier = new Mommifier();
String mommifiedWord = mommifier.mommify(word);
assertEquals("mommy", mommifiedWord);
}
}

45. SOURCE
public class Mommifier {
public String mommify(String word) {
for (char character : word.toCharArray()) {
if (character == 'a'
|| character == 'e'
|| character == 'i'
|| character == 'o'
|| character == 'u'){
return "mommy";
}
}
return word;
}
}

46. SOURCE
public class Mommifier {
private static final String VOWELS = "aeiou";
private static final String REPLACEMENT_WORD = "mommy";
public String mommify(String word) {
for (Character character : word.toCharArray()) {
if (isAVowel(character)) {
return REPLACEMENT_WORD;
}
}
return word;
}
private boolean isAVowel(Character character) {
return VOWELS.contains(character.toString());
}
}

47. TEST
import org.junit.Test;
import static org.junit.Assert.assertEquals;
public class MommifierTest {
@Test
public void shouldNotMommifyEmptyString() {...}
@Test
public void shouldNotMommifyWordsWithNoVowels() {...}
@Test
public void shouldMommifyVowel() {
String word = "a";
Mommifier mommifier = new Mommifier();
String mommifiedWord = mommifier.mommify(word);
assertEquals("mommy", mommifiedWord);
}
}

48. TEST
private Mommifier mommifier;
@Before
public void setUp() {
mommifier = new Mommifier();
}
@Test
public void shouldNotMommifyEmptyString() {
assertEquals("", mommifier.mommify(""));
}
@Test
public void shouldNotMommifyWordsWithNoVowels() {
assertEquals("str", mommifier.mommify("str"));
}
@Test
public void shouldMommifyVowel() {
assertEquals("mommy", mommifier.mommify("a"));
}

49. TEST
private Mommifier mommifier;
@Before
public void setUp() {
mommifier = new Mommifier();
}
@Test
public void shouldNotMommifyEmptyString() {
assertEquals("", mommifier.mommify(""));
}
@Test
public void shouldNotMommifyWordsWithNoVowels() {
assertEquals("str", mommifier.mommify("str"));
}
@Test
public void shouldMommifyVowel() {
assertEquals("mommy", mommifier.mommify("a"));
}

50. TEST
import ...;
public class MommifierTest {
private Mommifier mommifier;
@Before
public void setUp() {...}
@Test
public void shouldNotMommifyEmptyString() {...}
@Test
public void shouldNotMommifyWordsWithNoVowels() {...}
@Test
public void shouldMommifyVowel() {...}
@Test
public void shouldMommifyConsonantsAndSingleVowel() {
assertEquals("blmommy", mommifier.mommify("bla"));
}
}

51. TEST
import ...;
public class MommifierTest {
private Mommifier mommifier;
@Before
public void setUp() {...}
@Test
public void shouldNotMommifyEmptyString() {...}
@Test
public void shouldNotMommifyWordsWithNoVowels() {...}
@Test
public void shouldMommifyVowel() {...}
@Test
public void shouldMommifyConsonantsAndSingleVowel() {
assertEquals("blmommy", mommifier.mommify("bla"));
}
}

52. SOURCE
public class Mommifier {
private static final String VOWELS = "aeiou";
private static final String REPLACEMENT_WORD = "mommy";
public String mommify(String word) {
String mommifiedWord = "";
for (Character character : word.toCharArray()) {
if (isAVowel(character)) {
mommifiedWord += REPLACEMENT_WORD;
} else {
mommifiedWord += character;
}
}
return mommifiedWord;
}
private boolean isAVowel(Character character) {
return VOWELS.contains(character.toString());
}
}

53. TEST
import ...;
public class MommifierTest {
private Mommifier mommifier;
@Before
public void setUp() {...}
@Test
public void shouldNotMommifyEmptyString() {...}
@Test
public void shouldNotMommifyWordsWithNoVowels() {...}
@Test
public void shouldMommifyVowel() {...}
@Test
public void shouldMommifyConsonantsAndSingleVowel() {
assertEquals("blmommy", mommifier.mommify("bla"));
}
}

54. TEST
private Mommifier mommifier;
@Before
public void setUp() {...}
@Test
public void shouldNotMommifyEmptyString() {...}
@Test
public void shouldNotMommifyWordsWithNoVowels() {...}
@Test
public void shouldMommifyVowel() {...}
@Test
public void shouldMommifyConsonantsAndSingleVowel() {...}
@Test
public void shouldNotMommifyLessThan30PercentVowels() {
assertEquals("blah", mommifier.mommify("blah"));
}

55. TEST
private Mommifier mommifier;
@Before
public void setUp() {...}
@Test
public void shouldNotMommifyEmptyString() {...}
@Test
public void shouldNotMommifyWordsWithNoVowels() {...}
@Test
public void shouldMommifyVowel() {...}
@Test
public void shouldMommifyConsonantsAndSingleVowel() {...}
@Test
public void shouldNotMommifyLessThan30PercentVowels() {
assertEquals("blah", mommifier.mommify("blah"));
}

56. SOURCE
...
private static final double THRESHOLD = 0.3;
public String mommify(String word) {
int vowelCount = 0;
String mommifiedWord = "";
for (Character character : word.toCharArray()) {
if (isAVowel(character)) {
mommifiedWord += REPLACEMENT_WORD;
vowelCount++;
} else {
mommifiedWord += character;
}
}
if((double)vowelCount/word.toCharArray().length
< THRESHOLD){
return word;
}
return mommifiedWord;
}
...

57. TEST
private Mommifier mommifier;
@Before
public void setUp() {...}
@Test
public void shouldNotMommifyEmptyString() {...}
@Test
public void shouldNotMommifyWordsWithNoVowels() {...}
@Test
public void shouldMommifyVowel() {...}
@Test
public void shouldMommifyConsonantsAndSingleVowel() {...}
@Test
public void shouldNotMommifyLessThan30PercentVowels() {
assertEquals("blah", mommifier.mommify("blah"));
}

58. SOURCE
public String mommify(String word) {
if(vowelCountLessThanThreshold(word)){
return word;
}
return replaceVowels(word);
}
private boolean vowelCountLessThanThreshold(String word){...}
private String replaceVowels(String word) {...}
private boolean isAVowel(Character character) {...}

59. TEST
private Mommifier mommifier;
@Before
public void setUp() {...}
@Test
public void shouldNotMommifyEmptyString() {...}
@Test
public void shouldNotMommifyWordsWithNoVowels() {...}
@Test
public void shouldMommifyVowel() {...}
@Test
public void shouldMommifyConsonantsAndSingleVowel() {...}
@Test
public void shouldNotMommifyLessThan30PercentVowels() {
assertEquals("blah", mommifier.mommify("blah"));
}

60. TEST
private Mommifier mommifier;
@Before
public void setUp() {...}
@Test
public void shouldNotMommifyEmptyString() {...}
@Test
public void shouldNotMommifyWordsWithNoVowels() {...}
@Test
public void shouldMommifyVowel() {...}
@Test
public void shouldMommifyConsonantsAndSingleVowel() {...}
@Test
public void shouldNotMommifyLessThan30PercentVowels() {...}
@Test
public void shouldMommifyContinuousVowelsOnlyOnce() {
assertEquals("blmommyh”, mommifier.mommify("blaah"));
}

61. TEST
private Mommifier mommifier;
@Before
public void setUp() {...}
@Test
public void shouldNotMommifyEmptyString() {...}
@Test
public void shouldNotMommifyWordsWithNoVowels() {...}
@Test
public void shouldMommifyVowel() {...}
@Test
public void shouldMommifyConsonantsAndSingleVowel() {...}
@Test
public void shouldNotMommifyLessThan30PercentVowels() {...}
@Test
public void shouldMommifyContinuousVowelsOnlyOnce() {
assertEquals("blmommyh”, mommifier.mommify("blaah"));
}

62. SOURCE
...
public String mommify(String word) {...}
private String replaceVowels(String word) {
String mommifiedWord = "";
for (Character character : word.toCharArray()) {
if (!isVowel(character)) {
mommifiedWord += character;
} else if(!mommifiedWord.endsWith(REPLACEMENT_WORD)){
mommifiedWord += REPLACEMENT_WORD;
}
}
return mommifiedWord;
}
private boolean vowelCountLessThanThreshold(String word){...}
private boolean isVowel(Character character) {...}
...

63. TEST
private Mommifier mommifier;
@Before
public void setUp() {...}
@Test
public void shouldNotMommifyEmptyString() {...}
@Test
public void shouldNotMommifyWordsWithNoVowels() {...}
@Test
public void shouldMommifyVowel() {...}
@Test
public void shouldMommifyConsonantsAndSingleVowel() {...}
@Test
public void shouldNotMommifyLessThan30PercentVowels() {...}
@Test
public void shouldMommifyContinuousVowelsOnlyOnce() {
assertEquals("blmommyh”, mommifier.mommify("blaah"));
}

64. TEST
private Mommifier mommifier;
@Before
public void setUp() {...}
@Test
public void shouldNotMommifyEmptyString() {...}
@Test
public void shouldNotMommifyWordsWithNoVowels() {...}
@Test
public void shouldMommifyVowel() {...}
@Test
public void shouldMommifyConsonantsAndSingleVowel() {...}
@Test
public void shouldNotMommifyLessThan30PercentVowels() {...}
@Test
public void shouldMommifyContinuousVowelsOnlyOnce() {...}
@Test
public void shouldMommifyMultipleSetsOfVowels() {
assertEquals("blmommyhmommy”, mommifier.mommify("blaha"));
}

65. TEST
private Mommifier mommifier;
@Before
public void setUp() {...}
@Test
public void shouldNotMommifyEmptyString() {...}
@Test
public void shouldNotMommifyWordsWithNoVowels() {...}
@Test
public void shouldMommifyVowel() {...}
@Test
public void shouldMommifyConsonantsAndSingleVowel() {...}
@Test
public void shouldNotMommifyLessThan30PercentVowels() {...}
@Test
public void shouldMommifyContinuousVowelsOnlyOnce() {...}
@Test
public void shouldMommifyMultipleSetsOfVowels() {
assertEquals("blmommyhmommy”, mommifier.mommify("blaha"));
}

66. TEST
@Before
public void setUp() {...}
@Test
public void shouldNotMommifyEmptyString() {...}
@Test
public void shouldNotMommifyWordsWithNoVowels() {...}
@Test
public void shouldMommifyVowel() {...}
@Test
public void shouldMommifyConsonantsAndSingleVowel() {...}
@Test
public void shouldNotMommifyLessThan30PercentVowels() {...}
@Test
public void shouldMommifyContinuousVowelsOnlyOnce() {...}
@Test
public void shouldMommifyMultipleSetsOfVowels() {...}
@Test
public void shouldMommifyCapitalVowels() {
assertEquals("BLmommy", mommifier.mommify("BLA"));
}

67. TEST
@Before
public void setUp() {...}
@Test
public void shouldNotMommifyEmptyString() {...}
@Test
public void shouldNotMommifyWordsWithNoVowels() {...}
@Test
public void shouldMommifyVowel() {...}
@Test
public void shouldMommifyConsonantsAndSingleVowel() {...}
@Test
public void shouldNotMommifyLessThan30PercentVowels() {...}
@Test
public void shouldMommifyContinuousVowelsOnlyOnce() {...}
@Test
public void shouldMommifyMultipleSetsOfVowels() {...}
@Test
public void shouldMommifyCapitalVowels() {
assertEquals("BLmommy", mommifier.mommify("BLA"));
}

68. SOURCE
public class Mommifier {
private static final String VOWELS = "aeiou";
private static final String REPLACEMENT_WORD = "mommy";
private static final double THRESHOLD = 0.3;
public String mommify(String word) {...}
private String replaceVowels(String word) {...}
private boolean vowelCountLessThanThreshold(String word){...}
private boolean isVowel(Character character) {
Character lowerCase = Character.toLowerCase(character);
return VOWELS.contains(lowerCase.toString());
}
}

69. TEST
@Before
public void setUp() {...}
@Test
public void shouldNotMommifyEmptyString() {...}
@Test
public void shouldNotMommifyWordsWithNoVowels() {...}
@Test
public void shouldMommifyVowel() {...}
@Test
public void shouldMommifyConsonantsAndSingleVowel() {...}
@Test
public void shouldNotMommifyLessThan30PercentVowels() {...}
@Test
public void shouldMommifyContinuousVowelsOnlyOnce() {...}
@Test
public void shouldMommifyMultipleSetsOfVowels() {...}
@Test
public void shouldMommifyCapitalVowels() {
assertEquals("BLmommy", mommifier.mommify("BLA"));
}

70. TEST
@Test
public void shouldNotMommifyEmptyString() {...}
@Test
public void shouldNotMommifyWordsWithNoVowels() {...}
@Test
public void shouldMommifyVowel() {...}
@Test
public void shouldMommifyConsonantsAndSingleVowel() {...}
@Test
public void shouldNotMommifyLessThan30PercentVowels() {...}
@Test
public void shouldMommifyContinuousVowelsOnlyOnce() {...}
@Test
public void shouldMommifyMultipleSetsOfVowels() {...}
@Test
public void shouldMommifyCapitalVowels() {...}
@Test(expected = NullPointerException.class)
public void shouldErrorOnNull() {
mommifier.mommify(null);
}

71. TEST
@Test
public void shouldNotMommifyEmptyString() {...}
@Test
public void shouldNotMommifyWordsWithNoVowels() {...}
@Test
public void shouldMommifyVowel() {...}
@Test
public void shouldMommifyConsonantsAndSingleVowel() {...}
@Test
public void shouldNotMommifyLessThan30PercentVowels() {...}
@Test
public void shouldMommifyContinuousVowelsOnlyOnce() {...}
@Test
public void shouldMommifyMultipleSetsOfVowels() {...}
@Test
public void shouldMommifyCapitalVowels() {...}
@Test(expected = NullPointerException.class)
public void shouldErrorOnNull() {
mommifier.mommify(null);
}

72. TEST CASES
“” → “”
“str” → “str”
“a” → “mommy”
“blah” → “blah”
“bla” → “blmommy”
“blaa” → “blmommy”
“blaaha” → “blmommyhmommy”
“blA” → “blmommy”
Null → raise exception

73. TEST CASES
public void shouldNotMommifyEmptyString
public void shouldNotMommifyWordsWithNoVowels
public void shouldMommifyVowel
public void shouldMommifyConsonantsAndSingleVowel
public void shouldNotMommifyLessThan30PercentVowels
public void shouldMommifyContinuousVowelsOnlyOnce
public void shouldMommifyMultipleSetsOfVowels
public void shouldMommifyCapitalVowels
public void shouldErrorOnNull

74. TOP DOWN TESTING

75. SOME USEFUL BOOKS

76. THANK YOU
Gabriel Gavasso
Anand Iyengar
Thao Dang
Hung Dang
Mommifier Dojo by TWU team