Fake your test away: How to abuse your test doubles

Presented at RubyConf 2021 by Jenny Shih

https://rubyconf.com/program/sessions#session-1162

Transcript

1. @jenny_codes
   Fake your test away
   How to abuse your test doubles
   

   View Slide

2. @jenny_codes
   

   View Slide

3. @jenny_codes
   @ RubyConf Taiwan 2019
   

   View Slide

4. @jenny_codes
   @ RubyConf Taiwan 2019
   

   View Slide

5. @jenny_codes
   @ RubyConf Taiwan 2019
   

   View Slide

6. @jenny_codes
   Let’s talk about Douglas Adams
   

   View Slide

7. @jenny_codes
   Let’s talk about Douglas Adams
   source: https://www.wallpaper
   fl
   are.com/don-t-panic-text-decor-the-hitchhiker-s-guide-to-the-galaxy-wallpaper-pwpgv
   

   View Slide

8. @jenny_codes
   Let’s talk about Douglas Adams
   Three stages in human civilization:
   
   
   • Survival
   
   
   • Inquiry
   
   
   • Sophistication
   

   View Slide

9. @jenny_codes
   Let’s talk about Douglas Adams
   Three stages in human civilization:
   
   
   • Survival: How?
   
   
   • Inquiry: Why?
   
   
   • Sophistication: Where?
   

   View Slide

10. @jenny_codes
    Let’s talk about Douglas Adams
    Three stages in human civilization:
    
    
    • Survival: How can we eat?
    
    
    • Inquiry: Why?
    
    
    • Sophistication: Where?
    

    View Slide

11. @jenny_codes
    Let’s talk about Douglas Adams
    Three stages in human civilization:
    
    
    • Survival: How can we eat?
    
    
    • Inquiry: Why do we eat?
    
    
    • Sophistication: Where?
    

    View Slide

12. @jenny_codes
    Let’s talk about Douglas Adams
    Three stages in human civilization:
    
    
    • Survival: How can we eat?
    
    
    • Inquiry: Why do we eat?
    
    
    • Sophistication: Where shall we have lunch?
    

    View Slide

13. @jenny_codes
    Let’s talk about testing
    

    View Slide

14. @jenny_codes
    Three stages in my relationship with test doubles:
    Let’s talk about testing
    

    View Slide

15. @jenny_codes
    Three stages in my relationship with test doubles
    
    
    • Survival: How to use test doubles?
    
    
    Let’s talk about testing
    

    View Slide

16. @jenny_codes
    Three stages in my relationship with test doubles
    
    
    • Survival: How to use test doubles?
    
    
    • Inquiry: Why do I test?
    
    
    Let’s talk about testing
    

    View Slide

17. @jenny_codes
    Three stages in my relationship with test doubles
    
    
    • Survival: How to use test doubles?
    
    
    • Inquiry: Why do I test?
    
    
    • Sophistication: Where shall I begin to delete my old tests?
    
    
    Let’s talk about testing
    

    View Slide

18. @jenny_codes
    Outline
    • Unit tests, integration tests, and those in between
    
    
    • Integration-test wannabes
    
    
    • Helicopter unit tests
    
    
    • How to not abuse your test doubles?
    

    View Slide

19. @jenny_codes
    Outline
    • Unit tests, integration tests, and those in between
    
    
    • Integration-test wannabes
    
    
    • Helicopter unit tests
    
    
    • How to not abuse your test doubles?
    

    View Slide

20. @jenny_codes
    Test double
    

    View Slide

21. @jenny_codes
    Test double
    
    
    ├─ Stub
    
    
    ├─ Mock
    
    
    └─ Spy
    

    View Slide

22. @jenny_codes
    Subject
    

    View Slide

23. @jenny_codes
    Dependency
    

    View Slide

24. Imagine a perfect world
    

    View Slide

25. @jenny_codes
    Testing pyramid
    Unit tests
    Integration
    tests
    Acceptance
    tests
    

    View Slide

26. @jenny_codes
    Testing pyramid, reality edition
    Integration-test
    wannabes
    Helicopter
    unit tests
    Scream tests
    🤔 🤔
    🤔
    🤔
    

    View Slide

27. @jenny_codes
    Testing pyramid, reality edition
    Helicopter
    unit tests
    Scream tests
    🤔 🤔
    🤔
    🤔
    Integration-test
    wannabes
    

    View Slide

28. @jenny_codes
    Testing pyramid, reality edition
    Helicopter
    unit tests
    Scream tests
    🤔 🤔
    🤔
    🤔
    Integration-test
    wannabes
    

    View Slide

29. @jenny_codes
    Testing pyramid, reality edition
    Helicopter
    unit tests
    Scream tests
    🤔 🤔
    🤔
    🤔
    Integration-test
    wannabes
    

    View Slide

30. @jenny_codes
    Outline
    • Unit tests, integration tests, and those in between
    
    
    • Integration-test wannabes
    
    
    • Helicopter unit tests
    
    
    • How to not abuse your test doubles?
    

    View Slide

31. @jenny_codes
    A restaurant that serves French toast
    

    View Slide

32. @jenny_codes
    A restaurant that serves French toast
    

    View Slide

33. @jenny_codes
    A restaurant that serves French toast
    

    View Slide

34. @jenny_codes
    A restaurant that serves French toast
    

    View Slide

35. @jenny_codes
    A restaurant that serves French toast
    

    View Slide

36. @jenny_codes
    The test
    

    View Slide

37. @jenny_codes
    The test
    

    View Slide

38. @jenny_codes
    🤔
    The test
    

    View Slide

39. @jenny_codes
    

    View Slide

40. @jenny_codes
    🔎
    

    View Slide

41. @jenny_codes
    🔎
    

    View Slide

42. @jenny_codes
    🔎
    🚨
    

    View Slide

43. @jenny_codes
    

    View Slide

44. @jenny_codes
    

    View Slide

45. @jenny_codes
    

    View Slide

46. @jenny_codes
    

    View Slide

47. @jenny_codes
    

    View Slide

48. @jenny_codes
    

    View Slide

49. @jenny_codes
    

    View Slide

50. @jenny_codes
    

    View Slide

51. @jenny_codes
    ⛔
    

    View Slide

52. @jenny_codes
    

    View Slide

53. @jenny_codes
    

    View Slide

54. @jenny_codes
    

    View Slide

55. @jenny_codes
    Integration-test wannabes (n.)
    Tests with randomly inserted test doubles because the real objects are
    too awkward to deal with.
    

    View Slide

56. @jenny_codes
    ❌ Random doubles == Random test failures
    Integration-test wannabes
    

    View Slide

57. @jenny_codes
    One month later…
    

    View Slide

58. @jenny_codes
    One month later…
    FAILED
    

    View Slide

59. @jenny_codes
    Therapeutic Refactoring by Katrina Owen, Cascadia Ruby Conf 2012
    

    View Slide

60. @jenny_codes
    

    View Slide

61. @jenny_codes
    when I don’t have to modify
    100 random test failures for it
    

    View Slide

62. @jenny_codes
    ❌ Random doubles == Random test failures
    
    
    ❌ Decreased productivity
    Integration-test wannabes
    

    View Slide

63. Test doubles are contracts
    

    View Slide

64. @jenny_codes
    Outline
    • Unit tests, integration tests, and those in between
    
    
    • Integration-test wannabes
    
    
    • Helicopter unit tests
    
    
    • How to not abuse your test doubles?
    

    View Slide

65. @jenny_codes
    Restaurant Service: Cheese Panini
    

    View Slide

66. @jenny_codes
    

    View Slide

67. @jenny_codes
    

    View Slide

68. @jenny_codes
    

    View Slide

69. @jenny_codes
    

    View Slide

70. @jenny_codes
    Chef
    Waiter
    Restaurant
    
    
    Service
    The dependency graph
    Floor
    🛸
    🌝
    🐢
    Cupboard
    Fridge
    Bread
    Cheese
    class-level dependency
    instance-level dependency
    

    View Slide

71. @jenny_codes
    The dependency graph
    🙈
    🙈
    Chef
    Waiter
    Restaurant
    
    
    Service
    Cupboard
    Fridge
    Bread
    Cheese
    class-level dependency
    instance-level dependency
    test double
    🙈
    🙈
    🙈
    

    View Slide

72. @jenny_codes
    The dependency graph
    🙈
    🙈
    Chef
    Waiter
    Restaurant
    
    
    Service
    class-level dependency
    instance-level dependency
    test double
    🙈
    🙈
    🙈
    🙈
    🙈
    

    View Slide

73. @jenny_codes
    

    View Slide

74. @jenny_codes
    

    View Slide

75. @jenny_codes
    

    View Slide

76. @jenny_codes
    

    View Slide

77. @jenny_codes
    

    View Slide

78. @jenny_codes
    

    View Slide

79. @jenny_codes
    

    View Slide

80. @jenny_codes
    

    View Slide

81. @jenny_codes
    Helicopter unit tests (n.)
    Tests that try to control every implementation detail in the subject.
    

    View Slide

82. @jenny_codes
    ❌ Fake empire
    The helicopter unit tests
    

    View Slide

83. @jenny_codes https://media.giphy.com/media/IguL9zRYV20X1QeKuV/giphy.gif
    Production
    Your CI
    The helicopter unit tests
    

    View Slide

84. @jenny_codes
    ❌ Fake empire
    
    
    ❌ Brittle tests
    The helicopter unit tests
    

    View Slide

85. @jenny_codes
    ❌ Fake empire
    
    
    ❌ Brittle tests
    The helicopter unit tests
    GUARANTEED
    

    View Slide

86. @jenny_codes
    ❌ Fake empire
    
    
    ❌ Brittle tests
    
    
    The helicopter unit tests
    x N
    

    View Slide

87. @jenny_codes
    Outline
    • Unit tests, integration tests, and those in between
    
    
    • Integration-test wannabes
    
    
    • Helicopter unit tests
    
    
    • How to not abuse your test doubles?
    

    View Slide

88. @jenny_codes
    hard-to-use code == hard-to-write test
    easy-to-use code == easy-to-write test
    

    View Slide

89. @jenny_codes
    Tests are the first consumer of your API
    

    View Slide

90. @jenny_codes
    https://twitter.com/dan_abramov/status/1456265490754510848/photo/1
    Write an unit test
    that can’t catch errors
    Write an integration test
    that has holes it
    

    View Slide

91. @jenny_codes
    • 🎁
    
    
    • 🎁
    
    
    • 🎁
    How to not abuse your test doubles?
    

    View Slide

92. @jenny_codes
    • Use the Principle of Least Knowledge
    
    
    • 🎁
    
    
    • 🎁
    How to not abuse your test doubles?
    

    View Slide

93. @jenny_codes
    Principle of Least Knowledge
    Don’t talk to strangers
    

    View Slide

94. @jenny_codes
    Principle of Least Knowledge
    

    View Slide

95. @jenny_codes
    Principle of Least Knowledge
    Life Universe Everything
    Answer
    

    View Slide

96. @jenny_codes
    Principle of Least Knowledge
    Life Universe Everything
    Answer
    

    View Slide

97. @jenny_codes
    Principle of Least Knowledge
    Life Universe
    Answer
    Everything
    

    View Slide

98. @jenny_codes
    Principle of Least Knowledge
    Answer
    Everything
    Universe
    Life
    

    View Slide

99. @jenny_codes
    Principle of Least Knowledge
    Don’t talk to strangers
    
    
    Low coupling
    

    View Slide

100. @jenny_codes
     Principle of Least Knowledge
     Don’t talk to strangers
     
     
     Low coupling
     

     View Slide

101. @jenny_codes
     Principle of Least Knowledge
     Don’t talk to strangers
     
     
     Low coupling
     

     View Slide

102. @jenny_codes
     

     View Slide

103. @jenny_codes
     

     View Slide

104. @jenny_codes
     

     View Slide

105. @jenny_codes
     

     View Slide

106. @jenny_codes
     

     View Slide

107. @jenny_codes
     

     View Slide

108. @jenny_codes
     Use Principle of Least Knowledge: Result
     

     View Slide

109. @jenny_codes
     Use Principle of Least Knowledge: Result
     

     View Slide

110. @jenny_codes
     • Use the Principle of Least Knowledge
     
     
     • 🎁
     
     
     • 🎁
     How to not abuse your test doubles?
     

     View Slide

111. @jenny_codes
     How to not abuse your test doubles?
     • Use the Principle of Least Knowledge
     
     
     • Separate decisions and delegations.
     
     
     • 🎁
     

     View Slide

112. @jenny_codes
     Decision
     • Logic
     
     
     • Condition
     
     
     • Calculation
     • Dependency
     
     
     • Relationships
     Delegation
     

     View Slide

113. @jenny_codes
     

     View Slide

114. @jenny_codes
     = delegation
     = decision
     

     View Slide

115. @jenny_codes
     1. Get resources
     
     
     2. Prepare ingredients
     
     
     3. Make dish
     
     
     4. Serve dish
     

     View Slide

116. @jenny_codes
     1. Get resources
     

     View Slide

117. @jenny_codes
     1. Get resources
     
     
     2. Prepare ingredients
     
     
     3. Make dish
     
     
     4. Serve dish
     

     View Slide

118. @jenny_codes
     1. Get resources
     
     
     2. Prepare ingredients
     
     
     3. Make dish
     
     
     4. Serve dish
     => waiter
     => waiter
     => chef
     

     View Slide

119. @jenny_codes
     Separate decision and delegation: Result
     

     View Slide

120. @jenny_codes
     Separate decision and delegation: Result
     

     View Slide

121. @jenny_codes
     

     View Slide

122. @jenny_codes
     

     View Slide

123. @jenny_codes
     

     View Slide

124. @jenny_codes
     Separate decision and delegation: Result
     Arrange
     Act
     Assert
     

     View Slide

125. @jenny_codes
     Separate decision and delegation: Result
     

     View Slide

126. @jenny_codes
     Decision
     • Logic
     
     
     • Condition
     
     
     • Calculation
     
     
     • Unit test
     • Dependency
     
     
     • Relationships
     Delegation
     

     View Slide

127. @jenny_codes
     Decision
     • Logic
     
     
     • Condition
     
     
     • Calculation
     
     
     • Unit test
     • Dependency
     
     
     • Relationships
     
     
     • Integration test
     Delegation
     

     View Slide

128. @jenny_codes
     Testing pyramid with decision and delegation
     Unit tests
     Integration
     tests
     Acceptance
     tests
     Decisions
     Delegation
     

     View Slide

129. @jenny_codes
     How to not abuse your test doubles?
     • Use the Principle of Least Knowledge
     
     
     • Separate decisions and delegations
     
     
     • 🎁
     

     View Slide

130. @jenny_codes
     • Use the Principle of Least Knowledge
     
     
     • Separate decision and delegation
     
     
     • Make the dependencies really obvious
     How to not abuse your test doubles?
     

     View Slide

131. @jenny_codes
     All dependencies are equal,
     
     
     but some are more equal than others.
     

     View Slide

132. @jenny_codes
     All dependencies are equal,
     
     
     but some are more equal than others.
     the side-e
     ff
     ect free the rest
     

     View Slide

133. @jenny_codes
     All dependencies are equal,
     
     
     but some are more equal than others.
     the side-e
     ff
     ect free the rest
     🤤
     

     View Slide

134. @jenny_codes
     All dependencies are equal,
     
     
     but some are more equal than others.
     the side-e
     ff
     ect free the rest
     🤤 ⚠
     

     View Slide

135. @jenny_codes
     the side-e
     ff
     ect free
     🤤
     All dependencies are equal,
     
     
     but some are more equal than others.
     the rest
     ⚠
     ⚠
     ⚠
     ⚠
     ⚠
     ⚠⚠⚠
     ⚠
     

     View Slide

136. @jenny_codes
     Revisit serve_french_toast
     

     View Slide

137. @jenny_codes
     Chef
     Waiter
     Restaurant
     
     
     Service
     Floor
     🛸
     🌝
     🐢
     class-level dependency
     instance-level dependency
     Revisit serve_french_toast
     

     View Slide

138. @jenny_codes
     Revisit serve_french_toast
     Chef
     Waiter
     Restaurant
     
     
     Service
     Floor
     🛸
     🌝
     🐢
     class-level dependency
     instance-level dependency
     

     View Slide

139. @jenny_codes
     Revisit serve_french_toast
     Chef
     Waiter
     Restaurant
     
     
     Service
     Floor
     🛸
     🌝
     🐢
     class-level dependency
     instance-level dependency
     

     View Slide

140. @jenny_codes
     Revisit serve_french_toast
     Chef
     Waiter
     Restaurant
     
     
     Service
     Floor
     🛸
     🌝
     🐢
     class-level dependency
     instance-level dependency
     

     View Slide

141. @jenny_codes
     Revisit serve_french_toast
     Chef
     Waiter
     Restaurant
     
     
     Service
     Floor
     🛸
     🌝
     🐢
     class-level dependency
     instance-level dependency
     How to make those
     dependencies obvious?
     

     View Slide

142. @jenny_codes
     Revisit serve_french_toast
     Chef
     Waiter
     Restaurant
     
     
     Service
     Floor
     🛸
     🌝
     🐢
     class-level dependency
     instance-level dependency
     

     View Slide

143. @jenny_codes
     Chef
     Waiter
     Restaurant
     
     
     Service
     Floor
     🛸 🌝 🐢
     

     View Slide

144. @jenny_codes
     Chef
     Waiter
     Restaurant
     
     
     Service
     Floor
     🛸
     🌝
     🐢
     

     View Slide

145. @jenny_codes
     Chef
     Waiter
     Restaurant
     
     
     Service
     Floor
     🛸
     🌝
     🔻
     🐢
     Restaurant
     
     
     Repo
     

     View Slide

146. @jenny_codes
     Chef
     Waiter
     Restaurant
     
     
     Service
     Floor
     🛸
     🌝
     🔻
     🐢
     Restaurant
     
     
     Repo
     

     View Slide

147. @jenny_codes
     

     View Slide

148. @jenny_codes
     ⚠
     ⚠
     ⚠
     

     View Slide

149. @jenny_codes
     

     View Slide

150. @jenny_codes
     

     View Slide

151. @jenny_codes
     Make dependencies obvious: Result
     

     View Slide

152. @jenny_codes
     Make dependencies obvious: Result
     

     View Slide

153. @jenny_codes
     Make dependencies obvious: Result
     

     View Slide

154. @jenny_codes
     • Use the Principle of Least Knowledge
     
     
     • Separate decision and delegation
     
     
     • Make the dependencies really obvious
     How to not abuse your test doubles?
     

     View Slide

155. @jenny_codes
     Design your system
     
     
     so there’s no room to abuse your test doubles
     

     View Slide

156. One last thing
     

     View Slide

157. @jenny_codes
     Talks that inspire me
     • Gary Bernhardt: Boundaries
     
     
     • Justin Searls: Please don’t mock me
     
     
     • Justin Searls: How to stop hating your test
     
     
     • Katrina Owen: Therapeutic refactoring
     
     
     • All the talks by Sandi Metz really
     

     View Slide

158. @jenny_codes
     Books that inspire me
     • The Art of Unit Testing by Roy Osherove
     
     
     • Domain Modeling Made Functional by Scott Wlaschin
     
     
     • The Hitchhiker’s Guide to the Galaxy by Douglas Adams
     

     View Slide

159. @jenny_codes
     Talk to me!
     or just
     @jenny_codes
     

     View Slide