An overview of test-driven development including a brief scripted demo.

1. Realistic Test-Driven Development:Paying and PreventingTechnical Debt Rob Myers Agile Development Practices 11 November 2009 11 November 2009 © Rob Myers 2009 1

2. 11 November 2009 © Rob Myers 2009 2 Unit testing is sooooDEPRESSING

3. 11 November 2009 © Rob Myers 2009 3 TDD is fun, and provides much more than just unit-tests!

4. 11 November 2009 © Rob Myers 2009 4 from XP to ATDD & BDD

5. 11 November 2009 © Rob Myers 2009 5 waste

6. 11 November 2009 © Rob Myers 2009 6 #1 automation public static void Main() { Console.WriteLine( “I sure hope this works...” + myObject.Foo()); }

7. 11 November 2009 © Rob Myers 2009 7

8. 11 November 2009 © Rob Myers 2009 8 #2 Test-First We write a test before writing the code that makes it pass.

9. Why Wait? 11 November 2009 © Rob Myers 2009 9 Code Test Months Code Test Weeks Code Test Days Code Test

10. What If? 11 November 2009 © Rob Myers 2009 10 Code Run Test Test Write Test Run Test Run Test Run Test

11. Benefits of Test-First Just-In-Time analysis. We know when something is… …done. …done correctly. …broken. …and fixed! 11 November 2009 © Rob Myers 2009 11

12. 11 November 2009 © Rob Myers 2009 12

13. 11 November 2009 © Rob Myers 2009 13 #3 Any behavior-preserving change that improves maintainability.

14. 11 November 2009 © Rob Myers 2009 14

15. 11 November 2009 © Rob Myers 2009 15

16. 11 November 2009 © Rob Myers 2009 16 #4 Mock Objects

18. Refactor all callers to use Earth (all?)

19. Extract abstract parent ‘Planet’

20. Planet needs a factory

21. Test that Mars adapter calls new Mars-map service (mock the service)

22. Test that Planet factory determines which planet client is on (mock config file)11 November 2009 © Rob Myers 2009 17 #5 A To-Do List

23. 11 November 2009 © Rob Myers 2009 18 Analogies & Metaphors

24. 11 November 2009 © Rob Myers 2009 19

25. 11 November 2009 © Rob Myers 2009 20

26. 11 November 2009 © Rob Myers 2009 21 “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

27. 11 November 2009 © Rob Myers 2009 22 real value

28. 11 November 2009 © Rob Myers 2009 23 architectural perspective

29. 11 November 2009 © Rob Myers 2009 24 roadblocks

30. 11 November 2009 © Rob Myers 2009 25 discipline

31. 11 November 2009 © Rob Myers 2009 26 steps Write oneunit test. Build or add to the object under test until everything compiles. Red: Watch the test fail! Green: Make all the tests pass by changing the object under test. Clean: Refactormercilessly! Repeat.

32. 11 November 2009 © Rob Myers 2009 27  given  when  then

33. 11 November 2009 © Rob Myers 2009 28 TDD Demo

34. 11 November 2009 © Rob Myers 2009 29 Basic UML Class Diagrams Foo - intprivateVariable + intPublicMethod() Bar Baz + void AbstractMethod( object parameter) - void PrivateMethod()

35. 11 November 2009 © Rob Myers 2009 30 Global Currency Money-Market Account

36. 11 November 2009 © Rob Myers 2009 31 Global ATMAccess

37. Stories As Rob the US account holder, I want to be able to withdraw USD from a US ATM, but select which currency holdings to withdraw from. As Rob, traveling in Europe, I want to be able to withdraw EUR from either my EUR holdings or my USD holdings. The default should be the most beneficial to me at the time. Shortly after the end of each month, I want to receive a report of my holdings and balance. The total balance should appear in the currency of my account address (USD). 11 November 2009 © Rob Myers 2009 32

38. Primary Objects 11 November 2009 © Rob Myers 2009 33 Currency Account Holding

39. More Detail 11 November 2009 © Rob Myers 2009 34 Currency Holding value currency currencyConverter CurrencyConverter convert value to another currency

41. When value is zero.11 November 2009 © Rob Myers 2009 35

42. Specification, and Interface 11 November 2009 © Rob Myers 2009 36 [TestMethod] public void GivesSameValueWhenSameCurrencyRequested() { CurrencyConverter converter = new CurrencyConverter(); string sameCurrency = "USD"; double sameValue = 100.0000; double converted = converter.convert( sameValue, sameCurrency, sameCurrency); Assert.AreEqual(sameValue, converted, 0.00004); } Will not compile. 

43. “Thank You, But…” 11 November 2009 © Rob Myers 2009 37 using System; class CurrencyConverter { public double convert( double value, string from, string to) { throw new NotImplementedException(); } }

44. “…I Want to See it Fail Successfully” 11 November 2009 © Rob Myers 2009 38 class CurrencyConverter { public double convert( double value, string from, string to) { return 0.0; } }

45. Just Enough to Pass 11 November 2009 © Rob Myers 2009 39 public double convert( double value, string from, string to) { return 100.0; }

46. a. Refactor Away the Duplication 11 November 2009 © Rob Myers 2009 40 [TestMethod] public void GivesSameValueWhenSameCurrencyRequested() { CurrencyConverter converter = new CurrencyConverter(); string sameCurrency = "USD"; double sameValue = 100.0000; double converted = converter.convert( sameValue, sameCurrency, sameCurrency); Assert.AreEqual(sameValue, converted, 0.00004); } public double convert( double value, string from, string to) { return 100.0; }

47. b. Triangulate 11 November 2009 © Rob Myers 2009 41

48. 11 November 2009 © Rob Myers 2009 42 We don’t add any behavior without a failing test… Rodin’s The Thinker, photo by CJ on Wikipedia

49. Triangulating Test 11 November 2009 © Rob Myers 2009 43 [TestMethod] public void GivesZeroWhenValueIsZero() { CurrencyConverter converter = new CurrencyConverter(); double zero = 0.0000; double converted = converter.convert( zero, "USD", "EUR"); Assert.AreEqual(zero, converted, 0.00004); }

50. Still “Cheating”? 11 November 2009 © Rob Myers 2009 44 class CurrencyConverter { public double convert( double value, string from, string to) { return value; } }

51. Maintain the Tests 11 November 2009 © Rob Myers 2009 45 [TestMethod] public void GivesZeroWhenValueIsZero() { CurrencyConverter converter = new CurrencyConverter(); // ... } [TestMethod] public void GivesSameValueWhenSameCurrencyRequested() { CurrencyConverter converter = new CurrencyConverter(); // ... }

52. TestInitialize Runs Before Each Test 11 November 2009 © Rob Myers 2009 46 private CurrencyConverter converter; [TestInitialize] public void InitConverter() { converter = new CurrencyConverter(); } [TestMethod] public void GivesZeroWhenValueIsZero() { // ... } [TestMethod] public void GivesSameValueWhenSameCurrencyRequested() { // ... }

53. What is the Expected Answer? 11 November 2009 © Rob Myers 2009 47 [TestMethod] public void ConvertsDollarsToEuros() { double converted = converter.convert( 100.0000, "USD", "EUR"); Assert.AreEqual(???, converted, 0.00004); }

54. Let’s “Guess”… 11 November 2009 © Rob Myers 2009 48 [TestMethod] public void ConvertsDollarsToEuros() { double converted = converter.convert( 100.0000, "USD", "EUR"); Assert.AreEqual(50.0000, converted, 0.00004); }

55. …Get it Working… 11 November 2009 © Rob Myers 2009 49 public double convert( double value, string from, string to) { if (to.Equals(from)) return value; return value * 0.5000; }

56. …Refactor… 11 November 2009 © Rob Myers 2009 50 public double convert( double value, string from, string to) { if (to.Equals(from)) return value; return value * ConversionRate(from, to); } private double ConversionRate(string from, string to) { return 0.5000; }

58. When value is zero.

59. Fix the hard-coded ConversionRate11 November 2009 © Rob Myers 2009 51

60. 11 November 2009 © Rob Myers 2009 52 Well, What is It??? Where does it come from?

61. Circumstantial Coupling? 11 November 2009 © Rob Myers 2009 53 CurrencyConverter

62. Managing the Transaction 11 November 2009 © Rob Myers 2009 54 Account CurrencyConverter Holding Holding Holding ConversionRates Holding

64. When value is zero.

65. Fix hard-coded ConversionRate().

66. Write ConversionRates.

67. Make a factory for ConversionRates that uses the FOREX.com Web Service.11 November 2009 © Rob Myers 2009 55

68. New Test Class 11 November 2009 © Rob Myers 2009 56 using Microsoft.VisualStudio.TestTools.UnitTesting; [TestClass] public class ConversionRatesTests { [TestMethod] public void StoresAndRetrievesRates() { ConversionRates rates = new ConversionRates(); string from = "USD"; string to = "EUR"; double rate = 0.7424; rates.PutRate(from, to, rate); Assert.AreEqual(rate, rates.GetRate(from, to)); } }

69. Fail 11 November 2009 © Rob Myers 2009 57 public class ConversionRates { public void PutRate(string from, string to, double rate) { } public double GetRate(string from, string to) { return 0.0; } }

70. No Need to be Coy 11 November 2009 © Rob Myers 2009 58 public class ConversionRates { private Dictionary<string, double> rates = new Dictionary<string, double>(); public void PutRate(string from, string to, double rate) { rates[from + to] = rate; } public double GetRate(string from, string to) { return rates[from + to]; } }

71. Isolate Behavior 11 November 2009 © Rob Myers 2009 59 public class ConversionRates { private Dictionary<string, double> rates = new Dictionary<string, double>(); public void PutRate(string from, string to, double rate) { rates[Key(from, to)] = rate; } public double GetRate(string from, string to) { return rates[Key(from, to)]; } private string Key(string from, string to) { return from + to; } }

73. When value is zero.

74. Fix hard-coded ConversionRate().

75. Write ConversionRates.

76. Make a factory for ConversionRates that uses the FOREX.com Web Service.11 November 2009 © Rob Myers 2009 60

77. Fix SetUp 11 November 2009 © Rob Myers 2009 61 [TestClass] public class CurrencyConverterTests { private CurrencyConverter converter; [TestInitialize] public void InitConverter() { ConversionRates rates = new ConversionRates(); rates.PutRate("USD", "EUR", 0.5000); converter = new CurrencyConverter(rates); }

78. Partially Refactored… 11 November 2009 © Rob Myers 2009 62 public class CurrencyConverter { private ConversionRates rates; public CurrencyConverter(ConversionRates rates) { this.rates = rates; } private double ConversionRate(string from, string to) { return 0.5000; }

79. Replace the Hard-Coded Value 11 November 2009 © Rob Myers 2009 63 public class CurrencyConverter { private ConversionRates rates; public CurrencyConverter(ConversionRates rates) { this.rates = rates; } private double ConversionRate(string from, string to) { return rates.GetRate(from, to); }

81. When value is zero.

82. Fix hard-coded ConversionRate().

83. Write ConversionRates.

84. Make a factory for ConversionRates that uses the FOREX.com Web Service.11 November 2009 © Rob Myers 2009 64

85. What is the Missing Piece? 11 November 2009 © Rob Myers 2009 65 ConversionRates rates = ConversionRates.ByAccountAnd???( account, ???);

87. ConversionRates returns 1/rate if inverse rate found.

88. ConversionRates throws when rate not found.11 November 2009 © Rob Myers 2009 66

89. Testing Exceptional Behavior 11 November 2009 © Rob Myers 2009 67 [TestMethod] public void ThrowsExceptionIfRateNotFound() { ConversionRates rates = new ConversionRates(); string from = "BAR"; string to = "BAZ"; try { rates.GetRate(from, to); Assert.Fail("should throw"); } catch (RateNotFoundException) { // expected } }

90. A New Exception 11 November 2009 © Rob Myers 2009 68 using System; public class RateNotFoundException : Exception { }

91. 11 November 2009 © Rob Myers 2009 69

92. Back in ConversionRates 11 November 2009 © Rob Myers 2009 70 public double GetRate(string from, string to) { if (!rates.ContainsKey(Key(from, to))) throw new RateNotFoundException(); return rates[Key(from, to)]; }

93. An Alternative Test 11 November 2009 © Rob Myers 2009 71 [TestMethod,ExpectedException(typeof(RateNotFoundException))] public void ThrowsExceptionIfRateNotFoundII() { ConversionRates rates = new ConversionRates(); string from = "BAR"; string to = "BAZ"; rates.GetRate(from, to); }

94. An Expressive Testfor an Expressive Exception 11 November 2009 © Rob Myers 2009 72 [TestMethod] public void ThrowsExceptionIfRateNotFound() { ConversionRates rates = new ConversionRates(); string from = "BAR"; string to = "BAZ"; try { rates.GetRate(from, to); Assert.Fail("should throw " + typeof(RateNotFoundException).Name); } catch (RateNotFoundExceptione) { StringAssert.Contains(e.Message, from); StringAssert.Contains(e.Message, to); } }

95. 11 November 2009 © Rob Myers 2009 73 Test-Driven Development: By Example Kent Beck Addison-Wesley, November 2002 Refactoring: Improving the Design of Existing Code Martin FowlerAddison-Wesley, July 1999 The Art of Agile Development James Shore & Shane Warden O'Reilly Media, October 2007 Rob.Myers@agileInstitute.com http://PowersOfTwo.agileInstitute.com/