Magic Tricks of Testing (AncientCityRuby)

Magic Tricks of Testing (AncientCityRuby)

Tests are supposed to save us money. How is it, then, that many times they become millstones around our necks, gradually morphing into fragile, breakable things that raise the cost of change?

We write too many tests and we test the wrong kinds of things. This talk strips away the veil and offers simple, practical guidelines for choosing what to test and how to test it. Finding the right testing balance isn’t magic, it’s a magic trick; come and learn the secret of writing stable tests that protect your application at the lowest possible cost.

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Sandi Metz

April 05, 2013
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Transcript

  1. @sandimetz Apr 2013 The Magic Tricks of Testing Sandi Metz

    Friday, April 5, 13
  2. @sandimetz Apr 2013 Why do I hate my tests? Friday,

    April 5, 13
  3. @sandimetz Apr 2013 Why do I hate my tests? Friday,

    April 5, 13
  4. @sandimetz Apr 2013 They’re slow. Friday, April 5, 13

  5. @sandimetz Apr 2013 They break every time I change something.

    Friday, April 5, 13
  6. @sandimetz Apr 2013 They cost more than they’re worth. Friday,

    April 5, 13
  7. @sandimetz Apr 2013 They are misery incarnate. Friday, April 5,

    13
  8. @sandimetz Apr 2013 It doesn’t have to be this way.

    Friday, April 5, 13
  9. @sandimetz Apr 2013 You just need to delete some tests.

    Friday, April 5, 13
  10. @sandimetz Apr 2013 Unit Tests: Goals Friday, April 5, 13

  11. @sandimetz Apr 2013 Thorough Unit Tests: Goals Friday, April 5,

    13
  12. @sandimetz Apr 2013 Thorough Stable Unit Tests: Goals Friday, April

    5, 13
  13. @sandimetz Apr 2013 Thorough Stable Fast Unit Tests: Goals Friday,

    April 5, 13
  14. @sandimetz Apr 2013 Thorough Stable Fast Few Unit Tests: Goals

    Friday, April 5, 13
  15. @sandimetz Apr 2013 What does your app feel like? Friday,

    April 5, 13
  16. @sandimetz Apr 2013 Friday, April 5, 13

  17. @sandimetz Apr 2013 Focus on messages. Friday, April 5, 13

  18. @sandimetz Apr 2013 Objects have a simple understanding of messages.

    Friday, April 5, 13
  19. @sandimetz Apr 2013 Object Under Test Friday, April 5, 13

  20. @sandimetz Apr 2013 Friday, April 5, 13

  21. @sandimetz Apr 2013 Object Under Test Friday, April 5, 13

  22. @sandimetz Apr 2013 Object Under Test Received from others Friday,

    April 5, 13
  23. @sandimetz Apr 2013 Object Under Test Received from others Friday,

    April 5, 13
  24. @sandimetz Apr 2013 Object Under Test Incoming Friday, April 5,

    13
  25. @sandimetz Apr 2013 Sent to others Incoming Object Under Test

    Friday, April 5, 13
  26. @sandimetz Apr 2013 Sent to others Incoming Object Under Test

    Friday, April 5, 13
  27. @sandimetz Apr 2013 Incoming Outgoing Object Under Test Friday, April

    5, 13
  28. @sandimetz Apr 2013 Sent to self Incoming Outgoing Object Under

    Test Friday, April 5, 13
  29. @sandimetz Apr 2013 Sent to self Incoming Outgoing Object Under

    Test Friday, April 5, 13
  30. @sandimetz Apr 2013 Incoming Sent to Self Outgoing Message Origin

    Friday, April 5, 13
  31. @sandimetz Apr 2013 Sent to self Incoming Outgoing Object Under

    Test Friday, April 5, 13
  32. @sandimetz Apr 2013 Sent to self Incoming Outgoing Object Under

    Test Friday, April 5, 13
  33. @sandimetz Apr 2013 Sent to self Incoming Outgoing Object Under

    Test Friday, April 5, 13
  34. @sandimetz Apr 2013 Sent to self Incoming Outgoing Query Command

    Object Under Test Friday, April 5, 13
  35. @sandimetz Apr 2013 Query Command Message Type Friday, April 5,

    13
  36. @sandimetz Apr 2013 Query: Returns something but changes nothing. Command:

    Returns nothing but changes something. Type Friday, April 5, 13
  37. @sandimetz Apr 2013 Query: Returns something but changes nothing. Command:

    Returns nothing but changes something. Type Friday, April 5, 13
  38. @sandimetz Apr 2013 Query: Returns something but changes nothing. Command:

    Returns nothing but changes something. Type Friday, April 5, 13
  39. @sandimetz Apr 2013 We conflate commands and queries at our

    peril. Friday, April 5, 13
  40. @sandimetz Apr 2013 But we do it all the time.

    Friday, April 5, 13
  41. @sandimetz Apr 2013 3 message Origins X 2 message Types

    Friday, April 5, 13
  42. Query Command Message Origin x Type Outgoing Incoming Type POV

    @sandimetz Apr 2013 Message Sent to Self Friday, April 5, 13
  43. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Outgoing Incoming

    Part 1 Incoming Friday, April 5, 13
  44. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Outgoing Incoming

    Incoming Query Messages Incoming Friday, April 5, 13
  45. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Outgoing Incoming

    Incoming Wheel diameter Friday, April 5, 13
  46. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Outgoing Incoming

    class  Wheel    attr_reader  :rim,  :tire    def  initialize(rim,  tire)    #  ...    end    def  diameter        rim  +  (tire  *  2)    end    #  ... Friday, April 5, 13
  47. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Outgoing Incoming

    class  Wheel    attr_reader  :rim,  :tire    def  initialize(rim,  tire)    #  ...    end    def  diameter        rim  +  (tire  *  2)    end    #  ... Friday, April 5, 13
  48. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Outgoing Incoming

    class  Wheel    attr_reader  :rim,  :tire    def  initialize(rim,  tire)    #  ...    end    def  diameter        rim  +  (tire  *  2)    end    #  ... Friday, April 5, 13
  49. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Outgoing Incoming

    class  WheelTest  <  MiniTest::Unit::TestCase    def  test_calculates_diameter        wheel  =  Wheel.new(26,  1.5)        assert_in_delta(29,                                        wheel.diameter,                                        0.01)    end end Friday, April 5, 13
  50. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Outgoing Incoming

    class  WheelTest  <  MiniTest::Unit::TestCase    def  test_calculates_diameter        wheel  =  Wheel.new(26,  1.5)        assert_in_delta(29,                                        wheel.diameter,                                        0.01)    end end Friday, April 5, 13
  51. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Outgoing Incoming

    class  WheelTest  <  MiniTest::Unit::TestCase    def  test_calculates_diameter        wheel  =  Wheel.new(26,  1.5)        assert_in_delta(29,                                        wheel.diameter,                                        0.01)    end end Friday, April 5, 13
  52. @sandimetz Apr 2013 Rule Friday, April 5, 13

  53. @sandimetz Apr 2013 Test incoming query messages Rule Friday, April

    5, 13
  54. @sandimetz Apr 2013 Test incoming query messages by making assertions

    about what they send back. Rule Friday, April 5, 13
  55. Query Command The Unit Testing Minimalist Incoming Type POV @sandimetz

    Apr 2013 Message Sent to Self Outgoing Friday, April 5, 13
  56. Query Command Assert result The Unit Testing Minimalist Incoming Type

    POV @sandimetz Apr 2013 Message Sent to Self Outgoing Friday, April 5, 13
  57. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Outgoing Incoming

    Incoming Another Incoming Query Message Friday, April 5, 13
  58. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Outgoing Incoming

    Gear gear_inches Incoming Friday, April 5, 13
  59. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Outgoing Incoming

    class  Gear    attr_reader  :chainring,  :cog,  :wheel    def  initialize(args)        #  ...    end      #  ...    def  gear_inches        ratio  *  wheel.diameter    end      private    def  ratio        chainring  /  cog.to_f    end      #  ... end Friday, April 5, 13
  60. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Outgoing Incoming

    class  Gear    attr_reader  :chainring,  :cog,  :wheel    def  initialize(args)        #  ...    end      #  ...    def  gear_inches        ratio  *  wheel.diameter    end      private    def  ratio        chainring  /  cog.to_f    end      #  ... end Friday, April 5, 13
  61. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Outgoing Incoming

    class  Gear    attr_reader  :chainring,  :cog,  :wheel    def  initialize(args)        #  ...    end      #  ...    def  gear_inches        ratio  *  wheel.diameter    end      private    def  ratio        chainring  /  cog.to_f    end      #  ... end Friday, April 5, 13
  62. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Outgoing Incoming

    class  Gear    attr_reader  :chainring,  :cog,  :wheel    def  initialize(args)        #  ...    end      #  ...    def  gear_inches        ratio  *  wheel.diameter    end      private    def  ratio        chainring  /  cog.to_f    end      #  ... end Friday, April 5, 13
  63. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Outgoing Incoming

    class  Gear    attr_reader  :chainring,  :cog,  :wheel    def  initialize(args)        #  ...    end      #  ...    def  gear_inches        ratio  *  wheel.diameter    end      private    def  ratio        chainring  /  cog.to_f    end      #  ... end Wheel Friday, April 5, 13
  64. @sandimetz Apr 2013 Sight along the edges of the space

    capsule. Friday, April 5, 13
  65. @sandimetz Apr 2013 Sight along the edges of the space

    capsule. Friday, April 5, 13
  66. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Outgoing Incoming

    class  GearTest  <  MiniTest::Unit::TestCase    def  test_calculates_gear_inches        gear  =    Gear.new(                            chainring:  52,                            cog:              11,                            wheel:          Wheel.new(26,  1.5))        assert_in_delta(137.1,                                        gear.gear_inches,                                        0.01)    end end Friday, April 5, 13
  67. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Outgoing Incoming

    class  GearTest  <  MiniTest::Unit::TestCase    def  test_calculates_gear_inches        gear  =    Gear.new(                            chainring:  52,                            cog:              11,                            wheel:          Wheel.new(26,  1.5))        assert_in_delta(137.1,                                        gear.gear_inches,                                        0.01)    end end Friday, April 5, 13
  68. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Outgoing Incoming

    class  GearTest  <  MiniTest::Unit::TestCase    def  test_calculates_gear_inches        gear  =    Gear.new(                            chainring:  52,                            cog:              11,                            wheel:          Wheel.new(26,  1.5))        assert_in_delta(137.1,                                        gear.gear_inches,                                        0.01)    end end Friday, April 5, 13
  69. @sandimetz Apr 2013 Test the interface, Friday, April 5, 13

  70. @sandimetz Apr 2013 Test the interface, not the implementation. Friday,

    April 5, 13
  71. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Outgoing Incoming

    Incoming Command Messages Incoming Friday, April 5, 13
  72. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Outgoing Incoming

    Gear set_cog Incoming Friday, April 5, 13
  73. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Outgoing Incoming

    class  Gear  attr_reader  :chainring,  :cog,  :wheel    def  initialize(args)        #  ...    end    def  set_cog(new_cog)        @cog  =  new_cog    end end Friday, April 5, 13
  74. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Outgoing Incoming

    class  Gear  attr_reader  :chainring,  :cog,  :wheel    def  initialize(args)        #  ...    end    def  set_cog(new_cog)        @cog  =  new_cog    end end Friday, April 5, 13
  75. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Outgoing Incoming

    class  Gear  attr_reader  :chainring,  :cog,  :wheel    def  initialize(args)        #  ...    end    def  set_cog(new_cog)        @cog  =  new_cog    end end Friday, April 5, 13
  76. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Outgoing Incoming

    class  GearTest  <  MiniTest::Unit::TestCase    def  test_set_cog        gear  =  Gear.new        gear.set_cog(27)        assert(27,  gear.cog)    end end Friday, April 5, 13
  77. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Outgoing Incoming

    class  GearTest  <  MiniTest::Unit::TestCase    def  test_set_cog        gear  =  Gear.new        gear.set_cog(27)        assert(27,  gear.cog)    end end Friday, April 5, 13
  78. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Outgoing Incoming

    class  GearTest  <  MiniTest::Unit::TestCase    def  test_set_cog        gear  =  Gear.new        gear.set_cog(27)        assert(27,  gear.cog)    end end Send the message Friday, April 5, 13
  79. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Outgoing Incoming

    class  GearTest  <  MiniTest::Unit::TestCase    def  test_set_cog        gear  =  Gear.new        gear.set_cog(27)        assert(27,  gear.cog)    end end Assert the side effect Friday, April 5, 13
  80. @sandimetz Apr 2013 Rule Friday, April 5, 13

  81. @sandimetz Apr 2013 Test incoming command messages Rule Friday, April

    5, 13
  82. @sandimetz Apr 2013 Test incoming command messages by making assertions

    about direct public side effects. Rule Friday, April 5, 13
  83. Query Command Assert result The Unit Testing Minimalist Incoming Type

    POV @sandimetz Apr 2013 Message Sent to Self Outgoing Friday, April 5, 13
  84. Query Command Assert result The Unit Testing Minimalist Incoming Type

    POV @sandimetz Apr 2013 Message Assert direct public side effects Sent to Self Outgoing Friday, April 5, 13
  85. @sandimetz Apr 2013 DRY It Out Friday, April 5, 13

  86. @sandimetz Apr 2013 Receiver of incoming message has sole responsibility

    DRY It Out Friday, April 5, 13
  87. @sandimetz Apr 2013 Receiver of incoming message has sole responsibility

    for asserting the result direct public side effects. DRY It Out Friday, April 5, 13
  88. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Outgoing Incoming

    Part 2 to Self Incoming Friday, April 5, 13
  89. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Outgoing Incoming

    to Self Incoming Messages Sent to Self Friday, April 5, 13
  90. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Outgoing Incoming

    class  Gear      #  ...    def  gear_inches        ratio  *  wheel.diameter    end      private    def  ratio        chainring  /  cog.to_f    end      #  ... end Friday, April 5, 13
  91. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Outgoing Incoming

    Anti-Pattern to Self Incoming Friday, April 5, 13
  92. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Outgoing Incoming

    class  GearTest  <  MiniTest::Unit::TestCase    def  test_calculates_ratio        gear  =    Gear.new(                            chainring:  52,                            cog:              11,                            wheel:          Wheel.new(26,  1.5))        assert_in_delta(4.7,                                        gear.ratio,                                        0.01)    end Friday, April 5, 13
  93. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Outgoing Incoming

    class  GearTest  <  MiniTest::Unit::TestCase    def  test_calculates_ratio        gear  =    Gear.new(                            chainring:  52,                            cog:              11,                            wheel:          Wheel.new(26,  1.5))        assert_in_delta(4.7,                                        gear.ratio,                                        0.01)    end Test the private method? Friday, April 5, 13
  94. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Outgoing Incoming

    class  GearTest  <  MiniTest::Unit::TestCase    def  test_calculates_ratio        gear  =    Gear.new(                            chainring:  52,                            cog:              11,                            wheel:          Wheel.new(26,  1.5))        assert_in_delta(4.7,                                        gear.ratio,                                        0.01)    end Friday, April 5, 13
  95. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Outgoing Incoming

    class  GearTest  <  MiniTest::Unit::TestCase    def  test_calculates_ratio        gear  =    Gear.new(                            chainring:  52,                            cog:              11,                            wheel:          Wheel.new(26,  1.5))        assert_in_delta(4.7,                                        gear.ratio,                                        0.01)    end Friday, April 5, 13
  96. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Outgoing Incoming

    class  GearTest  <  MiniTest::Unit::TestCase    def  test_calculates_ratio        gear  =    Gear.new(                            chainring:  52,                            cog:              11,                            wheel:          Wheel.new(26,  1.5))        assert_in_delta(4.7,                                        gear.ratio,                                        0.01)    end Redundant: Other tests already prove Gear works. Friday, April 5, 13
  97. Friday, April 5, 13

  98. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Outgoing Incoming

    Anti-Pattern to Self Incoming Friday, April 5, 13
  99. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Outgoing Incoming

    class  Gear      #  ...    def  gear_inches        ratio  *  wheel.diameter    end      private    def  ratio        chainring  /  cog.to_f    end      #  ... end Friday, April 5, 13
  100. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Outgoing Incoming

    class  Gear      #  ...    def  gear_inches        ratio  *  wheel.diameter    end      private    def  ratio        chainring  /  cog.to_f    end      #  ... end Friday, April 5, 13
  101. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Outgoing Incoming

    class  Gear      #  ...    def  gear_inches        ratio  *  wheel.diameter    end      private    def  ratio        chainring  /  cog.to_f    end      #  ... end Friday, April 5, 13
  102. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Outgoing Incoming

    class  GearTest  <  MiniTest::Unit::TestCase    def  test_calculates_gear_inches        gear  =    Gear.new(                            chainring:  52,                            cog:              11,                            wheel:          Wheel.new(26,  1.5))        assert_in_delta(137.1,                                        gear.gear_inches,                                        0.01)    end end Friday, April 5, 13
  103. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Outgoing Incoming

    class  GearTest  <  MiniTest::Unit::TestCase    def  test_calculates_gear_inches        gear  =    Gear.new(                            chainring:  52,                            cog:              11,                            wheel:          Wheel.new(26,  1.5))        assert_in_delta(137.1,                                        gear.gear_inches,                                        0.01)        gear.expect(:ratio)        gear.verify    end Friday, April 5, 13
  104. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Outgoing Incoming

    class  GearTest  <  MiniTest::Unit::TestCase    def  test_calculates_gear_inches        gear  =    Gear.new(                            chainring:  52,                            cog:              11,                            wheel:          Wheel.new(26,  1.5))        assert_in_delta(137.1,                                        gear.gear_inches,                                        0.01)        gear.expect(:ratio)        gear.verify    end Expect to send the private method? Friday, April 5, 13
  105. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Outgoing Incoming

    class  GearTest  <  MiniTest::Unit::TestCase    def  test_calculates_gear_inches        gear  =    Gear.new(                            chainring:  52,                            cog:              11,                            wheel:          Wheel.new(26,  1.5))        assert_in_delta(137.1,                                        gear.gear_inches,                                        0.01)        gear.expect(:ratio)        gear.verify    end Over Speci ed: Adds no safety yet breaks every time the implementation changes. Friday, April 5, 13
  106. Friday, April 5, 13

  107. @sandimetz Apr 2013 Rule Friday, April 5, 13

  108. @sandimetz Apr 2013 Do not test private methods. Rule Friday,

    April 5, 13
  109. @sandimetz Apr 2013 Do not test private methods. Do not

    make assertions about their result. Rule Friday, April 5, 13
  110. @sandimetz Apr 2013 Do not test private methods. Do not

    make assertions about their result. Do not expect to send them. Rule Friday, April 5, 13
  111. @sandimetz Apr 2013 Temporarily breaking this rule can save $$$

    during development. Caveat Friday, April 5, 13
  112. Query Command Assert result Assert direct public side-effects The Unit

    Testing Minimalist Incoming Type POV @sandimetz Apr 2013 Message Sent to Self Outgoing Friday, April 5, 13
  113. Query Command Assert result Assert direct public side-effects The Unit

    Testing Minimalist Incoming Type POV @sandimetz Apr 2013 Ignore Message Sent to Self Outgoing Friday, April 5, 13
  114. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Outgoing Incoming

    Part 3 Outgoing to Self Incoming Friday, April 5, 13
  115. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Outgoing Incoming

    Outgoing to Self Incoming Outgoing Query Messages Friday, April 5, 13
  116. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Outgoing Incoming

    Outgoing to Self Incoming Spoiler Alert Same rules as ‘Sent to Self’ Friday, April 5, 13
  117. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Outgoing Incoming

    diameter Gear gear_inches Wheel Outgoing to Self Incoming Friday, April 5, 13
  118. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Outgoing Incoming

    class  Gear    attr_reader  :chainring,  :cog,  :wheel    def  initialize(args)          #  ...    end    def  gear_inches        ratio  *  wheel.diameter    end      private    def  ratio        chainring  /  cog.to_f    end      #  ... end Outgoing to Self Incoming Friday, April 5, 13
  119. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Outgoing Incoming

    class  Gear    attr_reader  :chainring,  :cog,  :wheel    def  initialize(args)          #  ...    end    def  gear_inches        ratio  *  wheel.diameter    end      private    def  ratio        chainring  /  cog.to_f    end      #  ... end Outgoing to Self Incoming Wheel Friday, April 5, 13
  120. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Outgoing Incoming

    Gear Gear Outgoing Wheel diameter Incoming Query Outgoing to Self Incoming gear_inches Friday, April 5, 13
  121. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Outgoing Incoming

    Anti-Pattern to Self Incoming Outgoing to Self Incoming Friday, April 5, 13
  122. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Incoming Outgoing

    class  GearTest  <  MiniTest::Unit::TestCase    def  test_calculates_gear_inches        gear  =    Gear.new(                            chainring:  52,                            cog:              11,                            wheel:          Wheel.new(26,  1.5))        assert_in_delta(137.1,                                        gear.gear_inches,                                        0.01)    end end Friday, April 5, 13
  123. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Incoming Outgoing

    class  GearTest  <  MiniTest::Unit::TestCase    def  test_calculates_gear_inches        gear  =    Gear.new(                            chainring:  52,                            cog:              11,                            wheel:          Wheel.new(26,  1.5))        assert_in_delta(137.1,                                        gear.gear_inches,                                        0.01)          assert_in_delta(29,                                        gear.wheel.diameter,                                        0.01)    end end Friday, April 5, 13
  124. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Incoming Outgoing

    class  GearTest  <  MiniTest::Unit::TestCase    def  test_calculates_gear_inches        gear  =    Gear.new(                            chainring:  52,                            cog:              11,                            wheel:          Wheel.new(26,  1.5))        assert_in_delta(137.1,                                        gear.gear_inches,                                        0.01)          assert_in_delta(29,                                        gear.wheel.diameter,                                        0.01)    end end Assert result of outgoing query? Friday, April 5, 13
  125. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Incoming Outgoing

    class  GearTest  <  MiniTest::Unit::TestCase    def  test_calculates_gear_inches        gear  =    Gear.new(                            chainring:  52,                            cog:              11,                            wheel:          Wheel.new(26,  1.5))        assert_in_delta(137.1,                                        gear.gear_inches,                                        0.01)          assert_in_delta(29,                                        gear.wheel.diameter,                                        0.01)    end end Redundant: This duplicates Wheel’s tests. Friday, April 5, 13
  126. Friday, April 5, 13

  127. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Outgoing Incoming

    Anti-Pattern to Self Incoming Outgoing to Self Incoming Friday, April 5, 13
  128. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Incoming Outgoing

    class  GearTest  <  MiniTest::Unit::TestCase    def  test_calculates_gear_inches        gear  =    Gear.new(                            chainring:  52,                            cog:              11,                            wheel:          Wheel.new(26,  1.5))        assert_in_delta(137.1,                                        gear.gear_inches,                                        0.01)          gear.wheel.expect(:diameter)        gear.verify    end end Friday, April 5, 13
  129. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Incoming Outgoing

    class  GearTest  <  MiniTest::Unit::TestCase    def  test_calculates_gear_inches        gear  =    Gear.new(                            chainring:  52,                            cog:              11,                            wheel:          Wheel.new(26,  1.5))        assert_in_delta(137.1,                                        gear.gear_inches,                                        0.01)          gear.wheel.expect(:diameter)        gear.verify    end end Expect to send outgoing query? Friday, April 5, 13
  130. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Incoming Outgoing

    class  GearTest  <  MiniTest::Unit::TestCase    def  test_calculates_gear_inches        gear  =    Gear.new(                            chainring:  52,                            cog:              11,                            wheel:          Wheel.new(26,  1.5))        assert_in_delta(137.1,                                        gear.gear_inches,                                        0.01)          gear.wheel.expect(:diameter)        gear.verify    end end Over Speci ed: Adds no safety yet breaks every time the implementation changes. Friday, April 5, 13
  131. Friday, April 5, 13

  132. @sandimetz Apr 2013 Rule Friday, April 5, 13

  133. @sandimetz Apr 2013 Rule Do not test outgoing query messages.

    Friday, April 5, 13
  134. @sandimetz Apr 2013 Rule Do not test outgoing query messages.

    Do not make assertions about their result. Friday, April 5, 13
  135. @sandimetz Apr 2013 Rule Do not test outgoing query messages.

    Do not make assertions about their result. Do not expect to send them. Friday, April 5, 13
  136. @sandimetz Apr 2013 If the message has no visible side-effects

    Friday, April 5, 13
  137. @sandimetz Apr 2013 If the message has no visible side-effects

    the sender should not test it. Friday, April 5, 13
  138. Query Command Assert result Assert direct public side effects The

    Unit Testing Minimalist Incoming Type POV @sandimetz Apr 2013 Message Ignore Sent to Self Outgoing Friday, April 5, 13
  139. Query Command Assert result Assert direct public side effects The

    Unit Testing Minimalist Incoming Type POV @sandimetz Apr 2013 Message Ignore Sent to Self Outgoing Friday, April 5, 13
  140. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Outgoing Incoming

    Outgoing Command Messages to Self Incoming Outgoing Friday, April 5, 13
  141. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Outgoing Incoming

    diameter gear_inches set_cog changed to Self Incoming Outgoing Wheel Gear Obs Friday, April 5, 13
  142. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Incoming Outgoing

    class  Gear    attr_reader  :chainring,  :cog,  :wheel    def  initialize(args)              #  ...      end    def  set_cog(new_cog)        @cog  =  new_cog    end end Change #set_cog to add observer. Friday, April 5, 13
  143. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Incoming Outgoing

    class  Gear    attr_reader  :chainring,  :cog,  :wheel    def  initialize(args)              #  ...      end    def  set_cog(new_cog)        @cog  =  new_cog    end end Friday, April 5, 13
  144. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Incoming Outgoing

    class  Gear    attr_reader  :chainring,  :cog,  :wheel,  :observer    def  initialize(args)              #  ...        @observer    =  args[:observer]    end    def  set_cog(new_cog)        @cog  =  new_cog    end end Friday, April 5, 13
  145. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Incoming Outgoing

    class  Gear      #  ...    def  set_cog(new_cog)        @cog  =  new_cog    end end Friday, April 5, 13
  146. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Incoming Outgoing

    class  Gear      #  ...    def  set_cog(new_cog)        @cog  =  new_cog    end end Friday, April 5, 13
  147. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Incoming Outgoing

    class  Gear      #  ...    def  set_cog(new_cog)        @cog  =  new_cog        changed        @cog    end    def  changed        observer.changed(chainring,  cog)    end end Friday, April 5, 13
  148. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Incoming Outgoing

    class  Gear      #  ...    def  set_cog(new_cog)        @cog  =  new_cog        changed        @cog    end    def  changed        observer.changed(chainring,  cog)    end end Friday, April 5, 13
  149. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Outgoing Incoming

    Gear set_cog changed Obs to Self Incoming Outgoing Friday, April 5, 13
  150. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Outgoing Incoming

    Gear set_cog changed Obs to Self Incoming Outgoing Side Effects Friday, April 5, 13
  151. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Outgoing Incoming

    changed Gear set_cog Obs Incoming Command to Self Incoming Outgoing Side Effects Friday, April 5, 13
  152. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Outgoing Incoming

    Gear Outgoing set_cog Obs changed Incoming Command to Self Incoming Outgoing Side Effects Friday, April 5, 13
  153. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Incoming Outgoing

    class  GearTest  <  MiniTest::Unit::TestCase    def  test_set_cog        gear  =  Gear.new        gear.set_cog(27)        assert(27,  gear.cog)    end end Make existing #set_cog test run. Friday, April 5, 13
  154. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Incoming Outgoing

    class  GearTest  <  MiniTest::Unit::TestCase    def  test_set_cog        gear  =  Gear.new                                                                                                                    @gear.set_cog(27)        assert(27,  @gear.cog)    end end Friday, April 5, 13
  155. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Incoming Outgoing

    class  GearTest  <  MiniTest::Unit::TestCase    def  test_set_cog        @observer  =  Obs.new        gear  =  Gear.new                                                                                                                    @gear.set_cog(27)        assert(27,  @gear.cog)    end end Friday, April 5, 13
  156. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Incoming Outgoing

    class  GearTest  <  MiniTest::Unit::TestCase    def  test_set_cog        @observer  =  Obs.new        @gear          =  Gear.new(                                    chainring:  52,                                    cog:              11,                                    observer:    @observer)        @gear.set_cog(27)        assert(27,  @gear.cog)    end end Friday, April 5, 13
  157. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Incoming Outgoing

    class  GearTest  <  MiniTest::Unit::TestCase    def  test_set_cog        @observer  =  Obs.new        @gear          =  Gear.new(                                    chainring:  52,                                    cog:              11,                                    observer:    @observer)        @gear.set_cog(27)        assert(27,  @gear.cog)    end end Runs real @observer#changed 1st version Friday, April 5, 13
  158. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Incoming Outgoing

    class  GearTest  <  MiniTest::Unit::TestCase    def  test_set_cog        @observer  =  Obs.new        @gear          =  Gear.new(                                    chainring:  52,                                    cog:              11,                                    observer:    @observer)        @observer.stub(:changed,  @gear.set_cog(27))  do            assert(27,  @gear.cog)        end    end end Variant Runs fake @observer#changed Friday, April 5, 13
  159. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Incoming Outgoing

    class  Gear        #  ...    def  set_cog(new_cog)        @cog  =  new_cog        changed        @cog    end    def  changed        observer.changed(chainring,  cog)    end end Friday, April 5, 13
  160. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Incoming Outgoing

    class  Gear        #  ...    def  set_cog(new_cog)        @cog  =  new_cog        changed        @cog    end    def  changed        observer.changed(chainring,  cog)    end end The app will be correct only if this message gets sent. Friday, April 5, 13
  161. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 Wheel Incoming Query changed

    Side Effects Gear Incoming Command Outgoing Obs Outgoing diameter gear_inches set_cog Friday, April 5, 13
  162. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 Side Effects Gear Wheel

    Obs Friday, April 5, 13
  163. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 Side Effects Gear Wheel

    Obs Friday, April 5, 13
  164. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 Side Effects Gear Wheel

    Obs Friday, April 5, 13
  165. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Outgoing Incoming

    Anti-Pattern to Self Incoming Outgoing Friday, April 5, 13
  166. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Incoming Outgoing

    class  GearTest  <  MiniTest::Unit::TestCase    def  test_saves_changed_cog_in_db        @observer  =  Obs.new        @gear          =  Gear.new(                                    chainring:  52,                                    cog:              11,                                    observer:    @observer)          @gear.set_cog(27)          #  assert  something  about  the  state  of  the  db    end end Friday, April 5, 13
  167. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Incoming Outgoing

    class  GearTest  <  MiniTest::Unit::TestCase    def  test_saves_changed_cog_in_db        @observer  =  Obs.new        @gear          =  Gear.new(                                    chainring:  52,                                    cog:              11,                                    observer:    @observer)          @gear.set_cog(27)          #  assert  something  about  the  state  of  the  db    end end Friday, April 5, 13
  168. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Incoming Outgoing

    class  GearTest  <  MiniTest::Unit::TestCase    def  test_saves_changed_cog_in_db        @observer  =  Obs.new        @gear          =  Gear.new(                                    chainring:  52,                                    cog:              11,                                    observer:    @observer)          @gear.set_cog(27)          #  assert  something  about  the  state  of  the  db    end end Friday, April 5, 13
  169. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Incoming Outgoing

    class  GearTest  <  MiniTest::Unit::TestCase    def  test_saves_changed_cog_in_db        @observer  =  Obs.new        @gear          =  Gear.new(                                    chainring:  52,                                    cog:              11,                                    observer:    @observer)          @gear.set_cog(27)          #  assert  something  about  the  state  of  the  db    end end Depends on the distant side effect. Friday, April 5, 13
  170. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Incoming Outgoing

    class  GearTest  <  MiniTest::Unit::TestCase    def  test_saves_changed_cog_in_db        @observer  =  Obs.new        @gear          =  Gear.new(                                    chainring:  52,                                    cog:              11,                                    observer:    @observer)          @gear.set_cog(27)          #  assert  something  about  the  state  of  the  db    end end Is this Gear’s responsibility? Friday, April 5, 13
  171. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Incoming Outgoing

    class  GearTest  <  MiniTest::Unit::TestCase    def  test_saves_changed_cog_in_db        @observer  =  Obs.new        @gear          =  Gear.new(                                    chainring:  52,                                    cog:              11,                                    observer:    @observer)          @gear.set_cog(27)          #  assert  something  about  the  state  of  the  db    end end Is this Gear’s responsibility? Friday, April 5, 13
  172. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Incoming Outgoing

    class  GearTest  <  MiniTest::Unit::TestCase    def  test_saves_changed_cog_in_db        @observer  =  Obs.new        @gear          =  Gear.new(                                    chainring:  52,                                    cog:              11,                                    observer:    @observer)          @gear.set_cog(27)          #  assert  something  about  the  state  of  the  db    end end This is an integration test. Friday, April 5, 13
  173. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Incoming Outgoing

    class  GearTest  <  MiniTest::Unit::TestCase    def  test_notifies_observers_when_cogs_change        @observer  =  MiniTest::Mock.new        @gear          =  Gear.new(                                    chainring:  52,                                    cog:              11,                                    observer:    @observer)        @observer.expect(:changed,  true,  [52,  27])        @gear.set_cog(27)        @observer.verify    end Friday, April 5, 13
  174. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Incoming Outgoing

    class  GearTest  <  MiniTest::Unit::TestCase    def  test_notifies_observers_when_cogs_change        @observer  =  MiniTest::Mock.new        @gear          =  Gear.new(                                    chainring:  52,                                    cog:              11,                                    observer:    @observer)        @observer.expect(:changed,  true,  [52,  27])        @gear.set_cog(27)        @observer.verify    end Friday, April 5, 13
  175. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Incoming Outgoing

    class  GearTest  <  MiniTest::Unit::TestCase    def  test_notifies_observers_when_cogs_change        @observer  =  MiniTest::Mock.new        @gear          =  Gear.new(                                    chainring:  52,                                    cog:              11,                                    observer:    @observer)        @observer.expect(:changed,  true,  [52,  27])        @gear.set_cog(27)        @observer.verify    end Friday, April 5, 13
  176. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Incoming Outgoing

    class  GearTest  <  MiniTest::Unit::TestCase    def  test_notifies_observers_when_cogs_change        @observer  =  MiniTest::Mock.new        @gear          =  Gear.new(                                    chainring:  52,                                    cog:              11,                                    observer:    @observer)        @observer.expect(:changed,  true,  [52,  27])        @gear.set_cog(27)        @observer.verify    end Friday, April 5, 13
  177. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Incoming Outgoing

    class  GearTest  <  MiniTest::Unit::TestCase    def  test_notifies_observers_when_cogs_change        @observer  =  MiniTest::Mock.new        @gear          =  Gear.new(                                    chainring:  52,                                    cog:              11,                                    observer:    @observer)        @observer.expect(:changed,  true,  [52,  27])        @gear.set_cog(27)        @observer.verify    end Friday, April 5, 13
  178. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Incoming Outgoing

    class  GearTest  <  MiniTest::Unit::TestCase    def  test_notifies_observers_when_cogs_change        @observer  =  MiniTest::Mock.new        @gear          =  Gear.new(                                    chainring:  52,                                    cog:              11,                                    observer:    @observer)        @observer.expect(:changed,  true,  [52,  27])        @gear.set_cog(27)        @observer.verify    end Friday, April 5, 13
  179. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Incoming Outgoing

    class  GearTest  <  MiniTest::Unit::TestCase    def  test_notifies_observers_when_cogs_change        @observer  =  MiniTest::Mock.new        @gear          =  Gear.new(                                    chainring:  52,                                    cog:              11,                                    observer:    @observer)        @observer.expect(:changed,  true,  [52,  27])        @gear.set_cog(27)        @observer.verify    end Depends on the interface. Friday, April 5, 13
  180. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Incoming Outgoing

    class  GearTest  <  MiniTest::Unit::TestCase    def  test_notifies_observers_when_cogs_change        @observer  =  MiniTest::Mock.new        @gear          =  Gear.new(                                    chainring:  52,                                    cog:              11,                                    observer:    @observer)        @observer.expect(:changed,  true,  [52,  27])        @gear.set_cog(27)        @observer.verify    end Gear is responsible for sending #changed to @observer. Friday, April 5, 13
  181. @sandimetz Apr 2013 Rule Friday, April 5, 13

  182. @sandimetz Apr 2013 Expect to send outgoing command messages. Rule

    Friday, April 5, 13
  183. @sandimetz Apr 2013 Breaking this rule can save $$$ if

    side effects are both stable and cheap. Caveat Friday, April 5, 13
  184. Query Command Assert result Assert direct public side effects Ignore

    The Unit Testing Minimalist Incoming Type POV @sandimetz Apr 2013 Message Ignore Sent to Self Outgoing Friday, April 5, 13
  185. Query Command Assert result Assert direct public side effects Ignore

    Expect to send The Unit Testing Minimalist Incoming Type POV @sandimetz Apr 2013 Message Ignore Sent to Self Outgoing Friday, April 5, 13
  186. @sandimetz Apr 2013 But Friday, April 5, 13

  187. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Incoming Outgoing

    class  GearTest  <  MiniTest::Unit::TestCase    def  test_notifies_observers_when_cogs_change        @observer  =  MiniTest::Mock.new        @gear          =  Gear.new(                                    chainring:  52,                                    cog:              11,                                    observer:    @observer)        @observer.expect(:changed,  true,  [52,  27])        @gear.set_cog(27)        @observer.verify    end What happens if the Observer class stops implementing #changed? Friday, April 5, 13
  188. @sandimetz Apr 2013 Stubs Friday, April 5, 13

  189. @sandimetz Apr 2013 Stubs Stubs de ne context. Friday, April

    5, 13
  190. @sandimetz Apr 2013 Stubs Stubs de ne context. Stub as

    needed (but zillions is a smell). Friday, April 5, 13
  191. @sandimetz Apr 2013 Stubs Stubs de ne context. Stub as

    needed (but zillions is a smell). Avoid stubbing in the object under test. Friday, April 5, 13
  192. @sandimetz Apr 2013 Stubs Stubs de ne context. Stub as

    needed (but zillions is a smell). Avoid stubbing in the object under test. Do not make assertions about stubs! Friday, April 5, 13
  193. @sandimetz Apr 2013 Mocks Friday, April 5, 13

  194. @sandimetz Apr 2013 Mocks Mocks test behavior. Friday, April 5,

    13
  195. @sandimetz Apr 2013 Mocks Mocks test behavior. Set expectations on

    mocks to test outgoing command messages. Friday, April 5, 13
  196. @sandimetz Apr 2013 Mocks Mocks test behavior. Set expectations on

    mocks to test outgoing command messages. One expectation per test (do your best). Friday, April 5, 13
  197. @sandimetz Apr 2013 Mocks Mocks test behavior. Set expectations on

    mocks to test outgoing command messages. One expectation per test (do your best). Do not stub using a mock! Friday, April 5, 13
  198. @sandimetz GoGaRuCo 2012 @sandimetz Apr 2013 to Self Incoming Outgoing

    class  GearTest  <  MiniTest::Unit::TestCase    def  test_notifies_observers_when_cogs_change        @observer  =  MiniTest::Mock.new        @gear          =  Gear.new(                                    chainring:  52,                                    cog:              11,                                    observer:    @observer)        @observer.expect(:changed,  true,  [52,  27])        @gear.set_cog(27)        @observer.verify    end So really, what happens if Observer stops implementing #changed? Friday, April 5, 13
  199. @sandimetz Apr 2013 Pain Friday, April 5, 13

  200. @sandimetz Apr 2013 API Drift Pain Friday, April 5, 13

  201. @sandimetz Apr 2013 Rule Friday, April 5, 13

  202. @sandimetz Apr 2013 Honor the contract. Rule Friday, April 5,

    13
  203. @sandimetz Apr 2013 Honor the contract. Ensure test doubles stay

    in sync with the API. Rule Friday, April 5, 13
  204. @sandimetz Apr 2013 Automagically  minitest  requires  that  stubbed  methods  exist

     https://github.com/benmoss/quacky  https://github.com/xaviershay/rspec-­‐fire  https://github.com/cfcosta/minitest-­‐firemock Friday, April 5, 13
  205. @sandimetz Apr 2013 Summary Friday, April 5, 13

  206. @sandimetz Apr 2013 Friday, April 5, 13

  207. @sandimetz Apr 2013 Friday, April 5, 13

  208. @sandimetz Apr 2013 Strive for Thorough, Stable Fast, Few Friday,

    April 5, 13
  209. @sandimetz Apr 2013 Test. Friday, April 5, 13

  210. @sandimetz Apr 2013 Test. Everything. Friday, April 5, 13

  211. @sandimetz Apr 2013 Test . Everything. Once. Friday, April 5,

    13
  212. @sandimetz Apr 2013 Test the interface, Friday, April 5, 13

  213. @sandimetz Apr 2013 Test the interface, not the implementation. Friday,

    April 5, 13
  214. @sandimetz Apr 2013 Guard against API drift. Friday, April 5,

    13
  215. Query Command Assert result Assert direct public side effects Ignore

    Expect to send Be a Minimalist Incoming Type POV @sandimetz Apr 2013 Message Ignore Sent to Self Outgoing Friday, April 5, 13
  216. @sandimetz Apr 2013 Use good judgement. Friday, April 5, 13

  217. @sandimetz Apr 2013 Insist on simplicity. Friday, April 5, 13

  218. @sandimetz Apr 2013 Practice the Tricks. Friday, April 5, 13

  219. @sandimetz Apr 2013 And go home every day saying... Friday,

    April 5, 13
  220. @sandimetz Apr 2013 I love my tests. Friday, April 5,

    13
  221. Thanks Sandi Metz @sandimetz Friday, April 5, 13

  222. http://www. ickr.com/photos/phil_shirley/5452562957/ thicket http://www. ickr.com/photos/zebble/6080622/ one padlock http://www. ickr.com/photos/chrisinplymouth/5543281168/ two

    padlocks http://www. ickr.com/photos/donjohnson395/2915304926/ twins at beach http://www.med.navy.mil/sites/nmcp/Patients/pediatrics/PublishingImages/binocular_boy.gif http://upload.wikimedia.org/wikipedia/commons/e/e1/Ordinary_bicycle02.jpg ordinary bike Magic Hat (82805980) Copyright Mmaxer - Shutterstock.com Dogs in Hats (39263399) Copyright MLoiselle - Fotolia.com Garden (35521385) Copyright Beboy - Fotolia.com Space Walk - Nasa http://grin.hq.nasa.gov/copyright.html Photo Credits Friday, April 5, 13
  223. @sandimetz Apr 2013 And one last time... http://poodr.info Friday, April

    5, 13
  224. @sandimetz Apr 2013 http://poodr.info Friday, April 5, 13

  225. @sandimetz Apr 2013 Hot off the press http://poodr.info Friday, April

    5, 13
  226. Questions? Friday, April 5, 13

  227. @sandimetz Apr 2013 http://poodr.info Friday, April 5, 13