TDD for the Win

TDD FOR THE WINBasics to Test Driven Development

May 2014 Minh Ngoc Dang

Senior Developer at ThoughtWorks

ThoughtWorks University Trainer

Minh Ngoc Dang

TESTING

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

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?

TEST DRIVEN DEVELOPMENT!

BUT WAIT…WHAT IS IT?

TEST DRIVING MEANS

Writing tests before writing code

Write the minimum amount of code necessary to make tests pass

Rinse and repeat

TESTS FIRST?! BUT WHY?

WHY TDD?

Back to previously posed questions

Test Coverage?

Cases Covered? Bug Prevention?

TEST COVERAGE

Tests written before code

TEST COVERAGE


Ensure all code covered by tests

TEST COVERAGE


Ensure all code covered by tests

High test coverage

WHY TDD?


Test Coverage?


TEST CASES

Test cases reflect exactly what code does

TEST CASES


Visible list of functionality

TEST CASES


Visible list of functionality

Easy to see which cases are missing

WHY TDD?


Test Coverage?


BUG PREVENTION

Mental shift in thinking up test case before code

BUG PREVENTION


Encourage edge case testing

BUG PREVENTION


Encourage edge case testing

Help prevent bugs in edge cases

WHY TDD?


Test Coverage?


AND THAT’S NOT ALL!

TIME SAVER

Ease in debugging

Confidence in refactoring

DRIVING DESIGN

Help define usage – How should the code be used?

Only write necessary code – YAGNI!

SO HOW CAN I TDD?

RED – GREEN - REFACTOR

New Test New Test New Test

Red

GreenRefactor

Red

GreenRefactor

Red

GreenRefactor

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

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 lettersNull → raise exception // null checks

TESTimport 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); } }

SOURCEpublic class Mommifier { public String mommify(String word) { return null; } }

SOURCEpublic class Mommifier { public String mommify(String word) { return ""; } }



@Test public void shouldNotMommifyEmptyString() {...} @Test public void shouldNotMommifyWordsWithNoVowels() { String word = "str";

Mommifier mommifier = new Mommifier(); String mommifiedWord = mommifier.mommify(word); assertEquals("str", mommifiedWord); }}

SOURCEpublic class Mommifier { public String mommify(String word) { return word; } }



@Test public void shouldNotMommifyEmptyString() {...} @Test public void shouldNotMommifyWordsWithNoVowels() { String word = "str";

Mommifier mommifier = new Mommifier(); String mommifiedWord = mommifier.mommify(word); assertEquals("str", mommifiedWord); }}



@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); }}

SOURCEpublic 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; }

}


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; }

}


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()); }

}

TESTprivate 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")); }

TESTimport ...;


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")); }}


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()); }}

TESTimport ...;


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")); }}


@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")); }

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; }

...

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) {...}


@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")); }

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 isVowel(Character character) {...}

...


@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")); }


@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")); }

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")); }


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 isVowel(Character character) { Character lowerCase = Character.toLowerCase(character); return VOWELS.contains(lowerCase.toString()); }}

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")); }

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); }

TEST CASES

“” → “”“str” → “str” “a” → “mommy”“blah” → “blah”“bla” → “blmommy” “blaa” → “blmommy”“blaaha” → “blmommyhmommy” “blA” → “blmommy”Null → raise exception

TEST CASES

public void shouldNotMommifyEmptyStringpublic void shouldNotMommifyWordsWithNoVowelspublic void shouldMommifyVowelpublic void shouldMommifyConsonantsAndSingleVowelpublic void shouldNotMommifyLessThan30PercentVowelspublic void shouldMommifyContinuousVowelsOnlyOncepublic void shouldMommifyMultipleSetsOfVowelspublic void shouldMommifyCapitalVowelspublic void shouldErrorOnNull

TOP DOWN TESTING

SOME USEFUL BOOKS

THANK YOU

Gabriel GavassoAnand Iyengar

Thao DangHung Dang

Mommifier Dojo by TWU team

TDD for the Win

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