The Magic Tricks of Testing - Sandi Metz

Transcript

1. @sandimetz May 2013 The Magic Tricks of Testing Sandi Metz Saturday, May 25, 2013
2. @sandimetz May 2013 Why do I hate my tests? Saturday, May 25, 2013
3. @sandimetz May 2013 Why do I hate my tests? Saturday, May 25, 2013
4. @sandimetz May 2013 They’re slow Saturday, May 25, 2013
5. @sandimetz May 2013 They’re fragile Saturday, May 25, 2013
6. @sandimetz May 2013 They’re expensive Saturday, May 25, 2013
7. @sandimetz May 2013 They are misery Saturday, May 25, 2013
8. @sandimetz May 2013 They are misery incarnate Saturday, May 25, 2013
9. @sandimetz May 2013 It doesn’t have to be this way Saturday, May 25, 2013
10. @sandimetz May 2013 Just delete some tests Saturday, May 25, 2013
11. @sandimetz May 2013 Unit Tests: Goals Saturday, May 25, 2013
12. @sandimetz May 2013 Thorough Unit Tests: Goals Saturday, May 25, 2013
13. @sandimetz May 2013 Thorough Stable Unit Tests: Goals Saturday, May 25, 2013
14. @sandimetz May 2013 Thorough Stable Fast Unit Tests: Goals Saturday, May 25, 2013
15. @sandimetz May 2013 Thorough Stable Fast Few Unit Tests: Goals Saturday, May 25, 2013
16. @sandimetz May 2013 How does your app feel? Saturday, May 25, 2013
17. @sandimetz May 2013 Saturday, May 25, 2013
18. @sandimetz May 2013 Focus on messages Saturday, May 25, 2013
19. @sandimetz May 2013 Objects are simple-minded Saturday, May 25, 2013
20. @sandimetz May 2013 Object Under Test Saturday, May 25, 2013
21. @sandimetz May 2013 Saturday, May 25, 2013
22. @sandimetz May 2013 Object Under Test Saturday, May 25, 2013
23. @sandimetz May 2013 Object Under Test Received from others Saturday, May 25, 2013
24. @sandimetz May 2013 Object Under Test Received from others Saturday, May 25, 2013
25. @sandimetz May 2013 Object Under Test Incoming Saturday, May 25, 2013
26. @sandimetz May 2013 Sent to others Incoming Object Under Test Saturday, May 25, 2013
27. @sandimetz May 2013 Sent to others Incoming Object Under Test Saturday, May 25, 2013
28. @sandimetz May 2013 Incoming Outgoing Object Under Test Saturday, May 25, 2013
29. @sandimetz May 2013 Sent to self Incoming Outgoing Object Under Test Saturday, May 25, 2013
30. @sandimetz May 2013 Sent to self Incoming Outgoing Object Under Test Saturday, May 25, 2013
31. @sandimetz May 2013 Incoming Sent to Self Outgoing Message Origin Saturday, May 25, 2013
32. @sandimetz May 2013 Sent to self Incoming Outgoing Object Under Test Saturday, May 25, 2013
33. @sandimetz May 2013 Sent to self Incoming Outgoing Object Under Test Saturday, May 25, 2013
34. @sandimetz May 2013 Sent to self Incoming Outgoing Object Under Test Saturday, May 25, 2013
35. @sandimetz May 2013 Sent to self Incoming Outgoing Query Command Object Under Test Saturday, May 25, 2013
36. @sandimetz May 2013 Query Command Message Type Saturday, May 25, 2013
37. @sandimetz May 2013 Query: Return something/ change nothing Command: Return nothing/ change something Type Saturday, May 25, 2013
38. @sandimetz May 2013 Query: Return something/ change nothing Command: Return nothing/ change something Type Saturday, May 25, 2013
39. @sandimetz May 2013 Query: Return something/ change nothing Command: Return nothing/ change something Type Saturday, May 25, 2013
40. @sandimetz May 2013 We conflate commands and queries at our peril Saturday, May 25, 2013
41. @sandimetz May 2013 but we do it all the time Saturday, May 25, 2013
42. Query Command Message Origin x Type Outgoing Incoming Type Origin @sandimetz May 2013 Message Sent to Self Saturday, May 25, 2013
43. @sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Outgoing Incoming Part 1 Incoming Saturday, May 25, 2013
44. @sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Outgoing Incoming Incoming Query Messages Incoming Saturday, May 25, 2013
45. @sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Outgoing Incoming Incoming Wheel diameter Saturday, May 25, 2013
46. @sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Outgoing Incoming class  Wheel    attr_reader  :rim,  :tire    def  initialize(rim,  tire)    #  ...    end    def  diameter        rim  +  (tire  *  2)    end    #  ... Saturday, May 25, 2013
47. @sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Outgoing Incoming class  Wheel    attr_reader  :rim,  :tire    def  initialize(rim,  tire)    #  ...    end    def  diameter        rim  +  (tire  *  2)    end    #  ... Saturday, May 25, 2013
48. @sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Outgoing Incoming class  Wheel    attr_reader  :rim,  :tire    def  initialize(rim,  tire)    #  ...    end    def  diameter        rim  +  (tire  *  2)    end    #  ... Saturday, May 25, 2013
49. @sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013
50. @sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013
51. @sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013
52. @sandimetz May 2013 Rule Saturday, May 25, 2013
53. @sandimetz May 2013 Test incoming query messages Rule Saturday, May 25, 2013
54. @sandimetz May 2013 Test incoming query messages by making assertions about what they send back Rule Saturday, May 25, 2013
55. Query Command The Unit Testing Minimalist Incoming Type @sandimetz May 2013 Message Sent to Self Outgoing Origin Saturday, May 25, 2013
56. Query Command Assert result The Unit Testing Minimalist Incoming Type @sandimetz May 2013 Message Sent to Self Outgoing Origin Saturday, May 25, 2013
57. @sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Outgoing Incoming Incoming Another Incoming Query Message Saturday, May 25, 2013
58. @sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Outgoing Incoming Gear gear_inches Incoming Saturday, May 25, 2013
59. @sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013
60. @sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013
61. @sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013
62. @sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013
63. @sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013
64. @sandimetz May 2013 Sight along the edges of the space capsule Saturday, May 25, 2013
65. @sandimetz May 2013 Sight along the edges of the space capsule Saturday, May 25, 2013
66. @sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013
67. @sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013
68. @sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013
69. @sandimetz May 2013 Test the interface Saturday, May 25, 2013
70. @sandimetz May 2013 Test the interface (not the implementation) Saturday, May 25, 2013
71. @sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Outgoing Incoming Incoming Command Messages Incoming Saturday, May 25, 2013
72. @sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Outgoing Incoming Gear set_cog Incoming Saturday, May 25, 2013
73. @sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013
74. @sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013
75. @sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013
76. @sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013
77. @sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013
78. @sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013
79. @sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013
80. @sandimetz May 2013 Rule Saturday, May 25, 2013
81. @sandimetz May 2013 Test incoming command messages Rule Saturday, May 25, 2013
82. @sandimetz May 2013 Test incoming command messages by making assertions about direct public side effects Rule Saturday, May 25, 2013
83. Query Command Assert result The Unit Testing Minimalist Incoming Type @sandimetz May 2013 Message Sent to Self Outgoing Origin Saturday, May 25, 2013
84. Query Command Assert result The Unit Testing Minimalist Incoming Type @sandimetz May 2013 Message Assert direct public side effects Sent to Self Outgoing Origin Saturday, May 25, 2013
85. @sandimetz May 2013 DRY It Out Saturday, May 25, 2013
86. @sandimetz May 2013 Receiver of incoming message has sole responsibility DRY It Out Saturday, May 25, 2013
87. @sandimetz May 2013 Receiver of incoming message has sole responsibility for asserting the result direct public side effects DRY It Out Saturday, May 25, 2013
88. @sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Outgoing Incoming Part 2 to Self Incoming Saturday, May 25, 2013
89. @sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Outgoing Incoming Messages Sent to Self to Self Incoming Saturday, May 25, 2013
90. @sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Outgoing Incoming class  Gear      #  ...    def  gear_inches        ratio  *  wheel.diameter    end      private    def  ratio        chainring  /  cog.to_f    end      #  ... end Saturday, May 25, 2013
91. @sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Outgoing Incoming Anti-Pattern to Self Incoming Saturday, May 25, 2013
92. @sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013
93. @sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013
94. @sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013
95. @sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013
96. @sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013
97. Saturday, May 25, 2013
98. @sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Outgoing Incoming Anti-Pattern to Self Incoming Saturday, May 25, 2013
99. @sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Outgoing Incoming class  Gear      #  ...    def  gear_inches        ratio  *  wheel.diameter    end      private    def  ratio        chainring  /  cog.to_f    end      #  ... end Saturday, May 25, 2013
100. @sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Outgoing Incoming class  Gear      #  ...    def  gear_inches        ratio  *  wheel.diameter    end      private    def  ratio        chainring  /  cog.to_f    end      #  ... end Saturday, May 25, 2013
101. @sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Outgoing Incoming class  Gear      #  ...    def  gear_inches        ratio  *  wheel.diameter    end      private    def  ratio        chainring  /  cog.to_f    end      #  ... end Saturday, May 25, 2013
102. @sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013
103. @sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013
104. @sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013
105. @sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013
106. Saturday, May 25, 2013
107. @sandimetz May 2013 Rule Saturday, May 25, 2013
108. @sandimetz May 2013 Do not test private methods Rule Saturday, May 25, 2013
109. @sandimetz May 2013 Do not test private methods Do not make assertions about their result Rule Saturday, May 25, 2013
110. @sandimetz May 2013 Do not test private methods Do not make assertions about their result Do not expect to send them Rule Saturday, May 25, 2013
111. @sandimetz May 2013 Break rule if it saves $$$ during development Caveat Saturday, May 25, 2013
112. Query Command Assert result Assert direct public side-effects The Unit Testing Minimalist Incoming Type @sandimetz May 2013 Message Sent to Self Outgoing Origin Saturday, May 25, 2013
113. Query Command Assert result Assert direct public side-effects The Unit Testing Minimalist Incoming Type @sandimetz May 2013 Ignore Message Sent to Self Outgoing Origin Saturday, May 25, 2013
114. @sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Outgoing Incoming Part 3 to Self Incoming Outgoing Saturday, May 25, 2013
115. @sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Outgoing Incoming Outgoing Query Messages to Self Incoming Outgoing Saturday, May 25, 2013
116. @sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Outgoing Incoming Spoiler Alert Same rules as ‘Sent to Self’ to Self Incoming Outgoing Saturday, May 25, 2013
117. @sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Outgoing Incoming diameter Gear gear_inches Wheel to Self Incoming Outgoing Saturday, May 25, 2013
118. @sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013
119. @sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013
120. @sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Outgoing Incoming Gear Gear Outgoing Wheel diameter Incoming Query gear_inches to Self Incoming Outgoing Saturday, May 25, 2013
121. @sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Outgoing Incoming Anti-Pattern to Self Incoming to Self Incoming Outgoing Saturday, May 25, 2013
122. @sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013
123. @sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013
124. @sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013
125. @sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013
126. Saturday, May 25, 2013
127. @sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Outgoing Incoming Anti-Pattern to Self Incoming to Self Incoming Outgoing Saturday, May 25, 2013
128. @sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013
129. @sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013
130. @sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013
131. Saturday, May 25, 2013
132. @sandimetz May 2013 Rule Saturday, May 25, 2013
133. @sandimetz May 2013 Rule Do not test outgoing query messages Saturday, May 25, 2013
134. @sandimetz May 2013 Rule Do not test outgoing query messages Do not make assertions about their result Saturday, May 25, 2013
135. @sandimetz May 2013 Rule Do not test outgoing query messages Do not make assertions about their result Do not expect to send them Saturday, May 25, 2013
136. @sandimetz May 2013 If a message has no visible side-effects Saturday, May 25, 2013
137. @sandimetz May 2013 If a message has no visible side-effects the sender should not test it Saturday, May 25, 2013
138. Query Command Assert result Assert direct public side effects The Unit Testing Minimalist Incoming Type @sandimetz May 2013 Message Ignore Sent to Self Outgoing Origin Saturday, May 25, 2013
139. Query Command Assert result Assert direct public side effects The Unit Testing Minimalist Incoming Type @sandimetz May 2013 Message Ignore Sent to Self Outgoing Origin Saturday, May 25, 2013
140. @sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Outgoing Incoming Outgoing Command Messages to Self Incoming Outgoing Saturday, May 25, 2013
141. @sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Outgoing Incoming diameter gear_inches set_cog changed Wheel Gear Obs to Self Incoming Outgoing Saturday, May 25, 2013
142. @sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013
143. @sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013
144. @sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013
145. @sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Incoming Outgoing class  Gear      #  ...    def  set_cog(new_cog)        @cog  =  new_cog    end end Saturday, May 25, 2013
146. @sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Incoming Outgoing class  Gear      #  ...    def  set_cog(new_cog)        @cog  =  new_cog    end end Saturday, May 25, 2013
147. @sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013
148. @sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013
149. @sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Outgoing Incoming Gear set_cog changed Obs to Self Incoming Outgoing Saturday, May 25, 2013
150. @sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Outgoing Incoming Gear set_cog changed Obs Side Effects to Self Incoming Outgoing Saturday, May 25, 2013
151. @sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Outgoing Incoming changed Gear set_cog Obs Incoming Command Side Effects to Self Incoming Outgoing Saturday, May 25, 2013
152. @sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Outgoing Incoming Gear Outgoing set_cog Obs changed Incoming Command Side Effects to Self Incoming Outgoing Saturday, May 25, 2013
153. @sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013
154. @sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013
155. @sandimetz GoGaRuCo 2012 @sandimetz May 2013 to Self Outgoing Incoming Anti-Pattern to Self Incoming Outgoing Saturday, May 25, 2013
156. @sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013
157. @sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013
158. @sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013
159. @sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013
160. @sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013
161. @sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013
162. @sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013
163. @sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013
164. @sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013
165. @sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013
166. @sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013
167. @sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013
168. @sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013
169. @sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013
170. @sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013
171. @sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013
172. @sandimetz May 2013 Rule Saturday, May 25, 2013
173. @sandimetz May 2013 Expect to send outgoing command messages Rule Saturday, May 25, 2013
174. @sandimetz May 2013 Break rule if side effects are stable and cheap Caveat Saturday, May 25, 2013
175. Query Command Assert result Assert direct public side effects Ignore The Unit Testing Minimalist Incoming Type @sandimetz May 2013 Message Ignore Sent to Self Outgoing Origin Saturday, May 25, 2013
176. Query Command Assert result Assert direct public side effects Ignore Expect to send The Unit Testing Minimalist Incoming Type @sandimetz May 2013 Message Ignore Sent to Self Outgoing Origin Saturday, May 25, 2013
177. @sandimetz May 2013 But Saturday, May 25, 2013
178. @sandimetz GoGaRuCo 2012 @sandimetz May 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, May 25, 2013
179. @sandimetz May 2013 Pain Saturday, May 25, 2013
180. @sandimetz May 2013 API Drift Pain Saturday, May 25, 2013
181. @sandimetz May 2013 Rule Saturday, May 25, 2013
182. @sandimetz May 2013 Honor the contract Rule Saturday, May 25, 2013
183. @sandimetz May 2013 Honor the contract Ensure test doubles stay in sync with the API Rule Saturday, May 25, 2013
184. @sandimetz May 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, May 25, 2013
185. @sandimetz May 2013 Summary Saturday, May 25, 2013
186. @sandimetz May 2013 Be a minimalist Saturday, May 25, 2013
187. Query Command Assert result Assert direct public side effects Ignore Expect to send Incoming Type @sandimetz May 2013 Message Ignore Sent to Self Outgoing Origin Saturday, May 25, 2013
188. @sandimetz May 2013 Use good judgement Saturday, May 25, 2013
189. @sandimetz May 2013 Test Saturday, May 25, 2013
190. @sandimetz May 2013 Test. Everything Saturday, May 25, 2013
191. @sandimetz May 2013 Test . Everything. Once Saturday, May 25, 2013
192. @sandimetz May 2013 Test the interface Saturday, May 25, 2013
193. @sandimetz May 2013 Trust collaborators Saturday, May 25, 2013
194. @sandimetz May 2013 Insist on simplicity Saturday, May 25, 2013
195. @sandimetz May 2013 Practice the Tricks Saturday, May 25, 2013
196. @sandimetz May 2013 Saturday, May 25, 2013
197. @sandimetz May 2013 Saturday, May 25, 2013
198. @sandimetz May 2013 I love my tests Saturday, May 25, 2013
199. Thanks Sandi Metz @sandimetz Saturday, May 25, 2013
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, May 25, 2013
201. @sandimetz May 2013 http://poodr.info Saturday, May 25, 2013
202. Questions? Saturday, May 25, 2013
203. @sandimetz May 2013 http://poodr.info Saturday, May 25, 2013