Magic Tricks of Testing (RailsConf)

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.

Transcript

1. @sandimetz Apr 2013
   The Magic Tricks of
   Testing
   Sandi Metz
   Saturday, April 27, 13
   

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2. @sandimetz Apr 2013
   Why do
   I hate my tests?
   Saturday, April 27, 13
   

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3. @sandimetz Apr 2013
   Why do
   I hate my tests?
   Saturday, April 27, 13
   

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4. @sandimetz Apr 2013
   They’re slow
   Saturday, April 27, 13
   

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5. @sandimetz Apr 2013
   They’re fragile
   Saturday, April 27, 13
   

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6. @sandimetz Apr 2013
   They’re expensive
   Saturday, April 27, 13
   

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7. @sandimetz Apr 2013
   They are misery
   Saturday, April 27, 13
   

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8. @sandimetz Apr 2013
   They are misery
   incarnate
   Saturday, April 27, 13
   

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9. @sandimetz Apr 2013
   It doesn’t have to be
   this way
   Saturday, April 27, 13
   

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10. @sandimetz Apr 2013
    Just delete some tests
    Saturday, April 27, 13
    

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11. @sandimetz Apr 2013
    Unit Tests: Goals
    Saturday, April 27, 13
    

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12. @sandimetz Apr 2013
    Thorough
    Unit Tests: Goals
    Saturday, April 27, 13
    

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13. @sandimetz Apr 2013
    Thorough
    Stable
    Unit Tests: Goals
    Saturday, April 27, 13
    

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14. @sandimetz Apr 2013
    Thorough
    Stable
    Fast
    Unit Tests: Goals
    Saturday, April 27, 13
    

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15. @sandimetz Apr 2013
    Thorough
    Stable
    Fast
    Few
    Unit Tests: Goals
    Saturday, April 27, 13
    

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16. @sandimetz Apr 2013
    How does your app
    feel?
    Saturday, April 27, 13
    

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17. @sandimetz Apr 2013
    Saturday, April 27, 13
    

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18. @sandimetz Apr 2013
    Focus on messages
    Saturday, April 27, 13
    

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19. @sandimetz Apr 2013
    Objects are
    simple-minded
    Saturday, April 27, 13
    

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20. @sandimetz Apr 2013
    Object
    Under
    Test
    Saturday, April 27, 13
    

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21. @sandimetz Apr 2013
    Saturday, April 27, 13
    

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22. @sandimetz Apr 2013
    Object
    Under
    Test
    Saturday, April 27, 13
    

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23. @sandimetz Apr 2013
    Object
    Under
    Test
    Received from
    others
    Saturday, April 27, 13
    

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24. @sandimetz Apr 2013
    Object
    Under
    Test
    Received from
    others
    Saturday, April 27, 13
    

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25. @sandimetz Apr 2013
    Object
    Under
    Test
    Incoming
    Saturday, April 27, 13
    

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26. @sandimetz Apr 2013
    Sent to
    others
    Incoming
    Object
    Under
    Test
    Saturday, April 27, 13
    

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27. @sandimetz Apr 2013
    Sent to
    others
    Incoming
    Object
    Under
    Test
    Saturday, April 27, 13
    

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28. @sandimetz Apr 2013
    Incoming Outgoing
    Object
    Under
    Test
    Saturday, April 27, 13
    

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29. @sandimetz Apr 2013
    Sent to self
    Incoming Outgoing
    Object
    Under
    Test
    Saturday, April 27, 13
    

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30. @sandimetz Apr 2013
    Sent to self
    Incoming Outgoing
    Object
    Under
    Test
    Saturday, April 27, 13
    

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31. @sandimetz Apr 2013
    Incoming
    Sent to Self
    Outgoing
    Message Origin
    Saturday, April 27, 13
    

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32. @sandimetz Apr 2013
    Sent to self
    Incoming Outgoing
    Object
    Under
    Test
    Saturday, April 27, 13
    

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33. @sandimetz Apr 2013
    Sent to self
    Incoming Outgoing
    Object
    Under
    Test
    Saturday, April 27, 13
    

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34. @sandimetz Apr 2013
    Sent to self
    Incoming Outgoing
    Object
    Under
    Test
    Saturday, April 27, 13
    

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35. @sandimetz Apr 2013
    Sent to self
    Incoming Outgoing
    Query Command
    Object
    Under
    Test
    Saturday, April 27, 13
    

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36. @sandimetz Apr 2013
    Query
    Command
    Message Type
    Saturday, April 27, 13
    

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37. @sandimetz Apr 2013
    Query: Return something/
    change nothing
    Command: Return nothing/
    change something
    Type
    Saturday, April 27, 13
    

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38. @sandimetz Apr 2013
    Query: Return something/
    change nothing
    Command: Return nothing/
    change something
    Type
    Saturday, April 27, 13
    

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39. @sandimetz Apr 2013
    Query: Return something/
    change nothing
    Command: Return nothing/
    change something
    Type
    Saturday, April 27, 13
    

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40. @sandimetz Apr 2013
    We conflate
    commands and queries
    at our peril
    Saturday, April 27, 13
    

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41. @sandimetz Apr 2013
    but
    we do it all the time
    Saturday, April 27, 13
    

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42. Query Command
    Message Origin x Type
    Outgoing
    Incoming
    Type
    Origin
    @sandimetz Apr 2013
    Message
    Sent to Self
    Saturday, April 27, 13
    

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43. @sandimetz GoGaRuCo 2012
    @sandimetz Apr 2013
    to Self Outgoing
    Incoming
    Part 1
    Incoming
    Saturday, April 27, 13
    

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44. @sandimetz GoGaRuCo 2012
    @sandimetz Apr 2013
    to Self Outgoing
    Incoming
    Incoming
    Query Messages
    Incoming
    Saturday, April 27, 13
    

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45. @sandimetz GoGaRuCo 2012
    @sandimetz Apr 2013
    to Self Outgoing
    Incoming
    Incoming
    Wheel
    diameter
    Saturday, April 27, 13
    

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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
       #  ...
    Saturday, April 27, 13
    

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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
       #  ...
    Saturday, April 27, 13
    

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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
       #  ...
    Saturday, April 27, 13
    

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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
    Saturday, April 27, 13
    

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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
    Saturday, April 27, 13
    

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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
    Saturday, April 27, 13
    

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52. @sandimetz Apr 2013
    Rule
    Saturday, April 27, 13
    

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53. @sandimetz Apr 2013
    Test incoming query messages
    Rule
    Saturday, April 27, 13
    

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54. @sandimetz Apr 2013
    Test incoming query messages
    by making assertions
    about what they send back
    Rule
    Saturday, April 27, 13
    

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55. Query Command
    The Unit Testing Minimalist
    Incoming
    Type
    @sandimetz Apr 2013
    Message
    Sent to Self
    Outgoing
    Origin
    Saturday, April 27, 13
    

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56. Query Command
    Assert
    result
    The Unit Testing Minimalist
    Incoming
    Type
    @sandimetz Apr 2013
    Message
    Sent to Self
    Outgoing
    Origin
    Saturday, April 27, 13
    

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57. @sandimetz GoGaRuCo 2012
    @sandimetz Apr 2013
    to Self Outgoing
    Incoming
    Incoming
    Another
    Incoming
    Query Message
    Saturday, April 27, 13
    

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58. @sandimetz GoGaRuCo 2012
    @sandimetz Apr 2013
    to Self Outgoing
    Incoming
    Gear
    gear_inches
    Incoming
    Saturday, April 27, 13
    

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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
    Saturday, April 27, 13
    

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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
    Saturday, April 27, 13
    

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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
    Saturday, April 27, 13
    

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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
    Saturday, April 27, 13
    

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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
    Saturday, April 27, 13
    

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64. @sandimetz Apr 2013
    Sight along the edges of
    the space capsule
    Saturday, April 27, 13
    

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65. @sandimetz Apr 2013
    Sight along the edges of
    the space capsule
    Saturday, April 27, 13
    

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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
    Saturday, April 27, 13
    

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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
    Saturday, April 27, 13
    

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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
    Saturday, April 27, 13
    

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69. @sandimetz Apr 2013
    Test the interface
    Saturday, April 27, 13
    

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70. @sandimetz Apr 2013
    Test the interface
    (not the implementation)
    Saturday, April 27, 13
    

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71. @sandimetz GoGaRuCo 2012
    @sandimetz Apr 2013
    to Self Outgoing
    Incoming
    Incoming
    Command Messages
    Incoming
    Saturday, April 27, 13
    

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72. @sandimetz GoGaRuCo 2012
    @sandimetz Apr 2013
    to Self Outgoing
    Incoming
    Gear
    set_cog
    Incoming
    Saturday, April 27, 13
    

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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
    Saturday, April 27, 13
    

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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
    Saturday, April 27, 13
    

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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
    Saturday, April 27, 13
    

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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
    Saturday, April 27, 13
    

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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
    Saturday, April 27, 13
    

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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
    Saturday, April 27, 13
    

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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
    Saturday, April 27, 13
    

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80. @sandimetz Apr 2013
    Rule
    Saturday, April 27, 13
    

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81. @sandimetz Apr 2013
    Test incoming command messages
    Rule
    Saturday, April 27, 13
    

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82. @sandimetz Apr 2013
    Test incoming command messages
    by making assertions
    about direct public side effects
    Rule
    Saturday, April 27, 13
    

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83. Query Command
    Assert
    result
    The Unit Testing Minimalist
    Incoming
    Type
    @sandimetz Apr 2013
    Message
    Sent to Self
    Outgoing
    Origin
    Saturday, April 27, 13
    

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84. Query Command
    Assert
    result
    The Unit Testing Minimalist
    Incoming
    Type
    @sandimetz Apr 2013
    Message
    Assert
    direct public
    side effects
    Sent to Self
    Outgoing
    Origin
    Saturday, April 27, 13
    

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85. @sandimetz Apr 2013
    DRY It Out
    Saturday, April 27, 13
    

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86. @sandimetz Apr 2013
    Receiver of incoming message
    has sole responsibility
    DRY It Out
    Saturday, April 27, 13
    

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87. @sandimetz Apr 2013
    Receiver of incoming message
    has sole responsibility
    for asserting
    the result
    direct public side effects
    DRY It Out
    Saturday, April 27, 13
    

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88. @sandimetz GoGaRuCo 2012
    @sandimetz Apr 2013
    to Self Outgoing
    Incoming
    Part 2
    to Self
    Incoming
    Saturday, April 27, 13
    

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89. @sandimetz GoGaRuCo 2012
    @sandimetz Apr 2013
    to Self Outgoing
    Incoming
    Messages Sent to Self
    to Self
    Incoming
    Saturday, April 27, 13
    

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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
    Saturday, April 27, 13
    

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91. @sandimetz GoGaRuCo 2012
    @sandimetz Apr 2013
    to Self Outgoing
    Incoming
    Anti-Pattern
    to Self
    Incoming
    Saturday, April 27, 13
    

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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
    Saturday, April 27, 13
    

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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?
    Saturday, April 27, 13
    

    View Slide

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
    Saturday, April 27, 13
    

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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
    Saturday, April 27, 13
    

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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:
    #gear_inches test is proof enough
    Saturday, April 27, 13
    

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97. Saturday, April 27, 13
    

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98. @sandimetz GoGaRuCo 2012
    @sandimetz Apr 2013
    to Self Outgoing
    Incoming
    Anti-Pattern
    to Self
    Incoming
    Saturday, April 27, 13
    

    View Slide

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
    Saturday, April 27, 13
    

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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
     Saturday, April 27, 13
     

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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
     Saturday, April 27, 13
     

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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
     Saturday, April 27, 13
     

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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
     Saturday, April 27, 13
     

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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?
     Saturday, April 27, 13
     

     View Slide

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 with every change
     Saturday, April 27, 13
     

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106. Saturday, April 27, 13
     

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107. @sandimetz Apr 2013
     Rule
     Saturday, April 27, 13
     

     View Slide

108. @sandimetz Apr 2013
     Do not test private methods
     Rule
     Saturday, April 27, 13
     

     View Slide

109. @sandimetz Apr 2013
     Do not test private methods
     Do not make assertions about their result
     Rule
     Saturday, April 27, 13
     

     View Slide

110. @sandimetz Apr 2013
     Do not test private methods
     Do not make assertions about their result
     Do not expect to send them
     Rule
     Saturday, April 27, 13
     

     View Slide

111. @sandimetz Apr 2013
     Break rule if it saves $$$
     during development
     Caveat
     Saturday, April 27, 13
     

     View Slide

112. Query Command
     Assert
     result
     Assert
     direct public
     side-effects
     The Unit Testing Minimalist
     Incoming
     Type
     @sandimetz Apr 2013
     Message
     Sent to Self
     Outgoing
     Origin
     Saturday, April 27, 13
     

     View Slide

113. Query Command
     Assert
     result
     Assert
     direct public
     side-effects
     The Unit Testing Minimalist
     Incoming
     Type
     @sandimetz Apr 2013
     Ignore
     Message
     Sent to Self
     Outgoing
     Origin
     Saturday, April 27, 13
     

     View Slide

114. @sandimetz GoGaRuCo 2012
     @sandimetz Apr 2013
     to Self Outgoing
     Incoming
     Part 3
     to Self
     Incoming Outgoing
     Saturday, April 27, 13
     

     View Slide

115. @sandimetz GoGaRuCo 2012
     @sandimetz Apr 2013
     to Self Outgoing
     Incoming
     Outgoing
     Query Messages
     to Self
     Incoming Outgoing
     Saturday, April 27, 13
     

     View Slide

116. @sandimetz GoGaRuCo 2012
     @sandimetz Apr 2013
     to Self Outgoing
     Incoming
     Spoiler Alert
     Same rules as ‘Sent to Self’
     to Self
     Incoming Outgoing
     Saturday, April 27, 13
     

     View Slide

117. @sandimetz GoGaRuCo 2012
     @sandimetz Apr 2013
     to Self Outgoing
     Incoming
     diameter
     Gear
     gear_inches
     Wheel
     to Self
     Incoming Outgoing
     Saturday, April 27, 13
     

     View Slide

118. @sandimetz GoGaRuCo 2012
     @sandimetz Apr 2013
     to Self
     Incoming Outgoing
     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
     Saturday, April 27, 13
     

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119. @sandimetz GoGaRuCo 2012
     @sandimetz Apr 2013
     to Self
     Incoming Outgoing
     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
     Saturday, April 27, 13
     

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120. @sandimetz GoGaRuCo 2012
     @sandimetz Apr 2013
     to Self Outgoing
     Incoming
     Gear
     Gear
     Outgoing
     Wheel
     diameter
     Incoming
     Query
     gear_inches
     to Self
     Incoming Outgoing
     Saturday, April 27, 13
     

     View Slide

121. @sandimetz GoGaRuCo 2012
     @sandimetz Apr 2013
     to Self Outgoing
     Incoming
     Anti-Pattern
     to Self
     Incoming to Self
     Incoming Outgoing
     Saturday, April 27, 13
     

     View Slide

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
     Saturday, April 27, 13
     

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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
     Saturday, April 27, 13
     

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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?
     Saturday, April 27, 13
     

     View Slide

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:
     Duplicates Wheel’s tests
     Saturday, April 27, 13
     

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126. Saturday, April 27, 13
     

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127. @sandimetz GoGaRuCo 2012
     @sandimetz Apr 2013
     to Self Outgoing
     Incoming
     Anti-Pattern
     to Self
     Incoming to Self
     Incoming Outgoing
     Saturday, April 27, 13
     

     View Slide

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
     Saturday, April 27, 13
     

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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?
     Saturday, April 27, 13
     

     View Slide

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 costs but not bene ts
     Saturday, April 27, 13
     

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131. Saturday, April 27, 13
     

     View Slide

132. @sandimetz Apr 2013
     Rule
     Saturday, April 27, 13
     

     View Slide

133. @sandimetz Apr 2013
     Rule
     Do not test
     outgoing query messages
     Saturday, April 27, 13
     

     View Slide

134. @sandimetz Apr 2013
     Rule
     Do not test
     outgoing query messages
     Do not make assertions about their result
     Saturday, April 27, 13
     

     View Slide

135. @sandimetz Apr 2013
     Rule
     Do not test
     outgoing query messages
     Do not make assertions about their result
     Do not expect to send them
     Saturday, April 27, 13
     

     View Slide

136. @sandimetz Apr 2013
     If a message has
     no visible side-effects
     Saturday, April 27, 13
     

     View Slide

137. @sandimetz Apr 2013
     If a message has
     no visible side-effects
     the sender
     should not test it
     Saturday, April 27, 13
     

     View Slide

138. Query Command
     Assert
     result
     Assert
     direct public
     side effects
     The Unit Testing Minimalist
     Incoming
     Type
     @sandimetz Apr 2013
     Message
     Ignore
     Sent to Self
     Outgoing
     Origin
     Saturday, April 27, 13
     

     View Slide

139. Query Command
     Assert
     result
     Assert
     direct public
     side effects
     The Unit Testing Minimalist
     Incoming
     Type
     @sandimetz Apr 2013
     Message
     Ignore
     Sent to Self
     Outgoing
     Origin
     Saturday, April 27, 13
     

     View Slide

140. @sandimetz GoGaRuCo 2012
     @sandimetz Apr 2013
     to Self Outgoing
     Incoming
     Outgoing
     Command Messages
     to Self
     Incoming Outgoing
     Saturday, April 27, 13
     

     View Slide

141. @sandimetz GoGaRuCo 2012
     @sandimetz Apr 2013
     to Self Outgoing
     Incoming
     diameter
     gear_inches
     set_cog
     changed
     Wheel
     Gear
     Obs
     to Self
     Incoming Outgoing
     Saturday, April 27, 13
     

     View Slide

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
     Saturday, April 27, 13
     

     View Slide

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
     Saturday, April 27, 13
     

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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
     Saturday, April 27, 13
     

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145. @sandimetz GoGaRuCo 2012
     @sandimetz Apr 2013
     to Self
     Incoming Outgoing
     class  Gear
          #  ...
        def  set_cog(new_cog)
            @cog  =  new_cog
        end
     end
     Saturday, April 27, 13
     

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146. @sandimetz GoGaRuCo 2012
     @sandimetz Apr 2013
     to Self
     Incoming Outgoing
     class  Gear
          #  ...
        def  set_cog(new_cog)
            @cog  =  new_cog
        end
     end
     Saturday, April 27, 13
     

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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
     Saturday, April 27, 13
     

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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
     Saturday, April 27, 13
     

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149. @sandimetz GoGaRuCo 2012
     @sandimetz Apr 2013
     to Self Outgoing
     Incoming
     Gear
     set_cog
     changed
     Obs
     to Self
     Incoming Outgoing
     Saturday, April 27, 13
     

     View Slide

150. @sandimetz GoGaRuCo 2012
     @sandimetz Apr 2013
     to Self Outgoing
     Incoming
     Gear
     set_cog
     changed
     Obs
     Side
     Effects
     to Self
     Incoming Outgoing
     Saturday, April 27, 13
     

     View Slide

151. @sandimetz GoGaRuCo 2012
     @sandimetz Apr 2013
     to Self Outgoing
     Incoming
     changed
     Gear
     set_cog
     Obs
     Incoming
     Command
     Side
     Effects
     to Self
     Incoming Outgoing
     Saturday, April 27, 13
     

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152. @sandimetz GoGaRuCo 2012
     @sandimetz Apr 2013
     to Self Outgoing
     Incoming
     Gear
     Outgoing
     set_cog
     Obs
     changed
     Incoming
     Command
     Side
     Effects
     to Self
     Incoming Outgoing
     Saturday, April 27, 13
     

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153. @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
     Saturday, April 27, 13
     

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154. @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
     This message MUST get sent
     Saturday, April 27, 13
     

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155. @sandimetz GoGaRuCo 2012
     @sandimetz Apr 2013
     to Self Outgoing
     Incoming
     Anti-Pattern
     to Self
     Incoming Outgoing
     Saturday, April 27, 13
     

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156. @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
     Saturday, April 27, 13
     

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157. @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
     Saturday, April 27, 13
     

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158. @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
     Saturday, April 27, 13
     

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159. @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
     Saturday, April 27, 13
     

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160. @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
     Saturday, April 27, 13
     

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161. @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?
     Saturday, April 27, 13
     

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162. @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?
     Saturday, April 27, 13
     

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163. @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
     Saturday, April 27, 13
     

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164. @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
     Saturday, April 27, 13
     

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165. @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
     Saturday, April 27, 13
     

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166. @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
     Saturday, April 27, 13
     

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167. @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
     Saturday, April 27, 13
     

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168. @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
     Saturday, April 27, 13
     

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169. @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
     Saturday, April 27, 13
     

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170. @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
     Saturday, April 27, 13
     

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171. @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
     Saturday, April 27, 13
     

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172. @sandimetz Apr 2013
     Rule
     Saturday, April 27, 13
     

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173. @sandimetz Apr 2013
     Expect to send
     outgoing command messages
     Rule
     Saturday, April 27, 13
     

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174. @sandimetz Apr 2013
     Break rule if side effects
     are stable and cheap
     Caveat
     Saturday, April 27, 13
     

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175. Query Command
     Assert
     result
     Assert
     direct public
     side effects
     Ignore
     The Unit Testing Minimalist
     Incoming
     Type
     @sandimetz Apr 2013
     Message
     Ignore
     Sent to Self
     Outgoing
     Origin
     Saturday, April 27, 13
     

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176. Query Command
     Assert
     result
     Assert
     direct public
     side effects
     Ignore Expect
     to send
     The Unit Testing Minimalist
     Incoming
     Type
     @sandimetz Apr 2013
     Message
     Ignore
     Sent to Self
     Outgoing
     Origin
     Saturday, April 27, 13
     

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177. @sandimetz Apr 2013
     But
     Saturday, April 27, 13
     

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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
     What happens if Observer
     stops implementing #changed?
     Saturday, April 27, 13
     

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179. @sandimetz Apr 2013
     Pain
     Saturday, April 27, 13
     

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180. @sandimetz Apr 2013
     API Drift
     Pain
     Saturday, April 27, 13
     

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181. @sandimetz Apr 2013
     Rule
     Saturday, April 27, 13
     

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182. @sandimetz Apr 2013
     Honor the contract
     Rule
     Saturday, April 27, 13
     

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183. @sandimetz Apr 2013
     Honor the contract
     Ensure test doubles stay in sync with the API
     Rule
     Saturday, April 27, 13
     

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184. @sandimetz Apr 2013
     Automagically
      minitest: requires that stubbed methods exist
      rspec: #should_receive(:msg).and_call_original
      https://github.com/psyho/bogus
      https://github.com/benmoss/quacky
      https://github.com/xaviershay/rspec-­‐fire
      https://github.com/cfcosta/minitest-­‐firemock
     Saturday, April 27, 13
     

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185. @sandimetz Apr 2013
     Summary
     Saturday, April 27, 13
     

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186. @sandimetz Apr 2013
     Be a
     minimalist
     Saturday, April 27, 13
     

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187. Query Command
     Assert
     result
     Assert
     direct public
     side effects
     Ignore Expect
     to send
     Incoming
     Type
     @sandimetz Apr 2013
     Message
     Ignore
     Sent to Self
     Outgoing
     Origin
     Saturday, April 27, 13
     

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188. @sandimetz Apr 2013
     Use good
     judgement
     Saturday, April 27, 13
     

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189. @sandimetz Apr 2013
     Test
     Saturday, April 27, 13
     

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190. @sandimetz Apr 2013
     Test.
     Everything
     Saturday, April 27, 13
     

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191. @sandimetz Apr 2013
     Test
     .
     Everything.
     Once
     Saturday, April 27, 13
     

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192. @sandimetz Apr 2013
     Test the
     interface
     Saturday, April 27, 13
     

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193. @sandimetz Apr 2013
     Trust
     collaborators
     Saturday, April 27, 13
     

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194. @sandimetz Apr 2013
     Insist on
     simplicity
     Saturday, April 27, 13
     

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195. @sandimetz Apr 2013
     Practice the Tricks
     Saturday, April 27, 13
     

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196. @sandimetz Apr 2013
     Saturday, April 27, 13
     

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197. @sandimetz Apr 2013
     Saturday, April 27, 13
     

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198. @sandimetz Apr 2013
     I love my tests
     Saturday, April 27, 13
     

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199. Thanks
     Sandi Metz
     @sandimetz
     Saturday, April 27, 13
     

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200. 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
     Saturday, April 27, 13
     

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201. @sandimetz Apr 2013
     http://poodr.info
     Saturday, April 27, 13
     

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202. Questions?
     Saturday, April 27, 13
     

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203. @sandimetz Apr 2013
     http://poodr.info
     Saturday, April 27, 13
     

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