Fake It While You Make It

We all write code to interface with external systems, like a web service or a message queue. Can you confidently write tests without requiring the system as a dependency? How can you shield users of your code from the inner workings of the interface? Explore one attempt to answer these questions.

There’s no shortage of tools at your disposal to solve these problems. This talk will introduce some available options, provide guidance on when one approach may be more appropriate than another, and discuss how to use these tools together to ease the testing process.

Transcript

1. Fake It While You Make It Kevin Murphy The Gnar Company @KEVIN_J_M
2. Third-Party Dependencies @KEVIN_J_M
3. @KEVIN_J_M
4. @KEVIN_J_M
5. 55 65 @KEVIN_J_M
6. 55 65 MA @KEVIN_J_M
7. Gnar Company Logo @KEVIN_J_M
8. @KEVIN_J_M
9. @KEVIN_J_M
10. @KEVIN_J_M
11. @KEVIN_J_M
12. SWEATHR
13. $11 Billion SWEATHR @KEVIN_J_M
14. $22 Billion? SWEATHR @KEVIN_J_M
15. SWEATHR Third-party dependency @KEVIN_J_M
16. HTTP API @KEVIN_J_M
17. @KEVIN_J_M
18. class Location end @KEVIN_J_M
19. class Location def sweater_weather? end end @KEVIN_J_M
20. class Location def sweater_weather? uri = URI(conditions_url_for_zip_code) end end @KEVIN_J_M
21. class Location def sweater_weather? uri = URI(conditions_url_for_zip_code) result = Net::HTTP.get(uri) end end @KEVIN_J_M
22. class Location def sweater_weather? uri = URI(conditions_url_for_zip_code) result = Net::HTTP.get(uri) response = JSON.parse(result) end end @KEVIN_J_M
23. class Location def sweater_weather? uri = URI(conditions_url_for_zip_code) result = Net::HTTP.get(uri) response = JSON.parse(result) feels_like = response.dig( “current_observation”, “feelslike_f”) end end @KEVIN_J_M
24. class Location def sweater_weather? uri = URI(conditions_url_for_zip_code) result = Net::HTTP.get(uri) response = JSON.parse(result) feels_like = response.dig( “current_observation”, “feelslike_f”) feels_like.to_f.between?(55, 65) end end @KEVIN_J_M
25. it "is time to break out the sweater" do location = Sweathr::Location.new( zip_code: “02108") expect(location.sweater_weather?).to be true end @KEVIN_J_M
26. > rspec spec/sweathr/location_spec.rb Failures: 1) Sweathr::Location#sweater_weather? is time to break out the sweater Failure/Error: expect(weather.sweater_weather?).to be true expected true got false Finished in 0.36974 seconds ( fi les took 0.2812 seconds to load) 1 example, 1 failure 70° F @KEVIN_J_M
27. > rspec spec/sweathr/location_spec.rb . Finished in 0.37186 seconds ( fi les took 0.48152 seconds to load) 1 example, 0 failures 63° F @KEVIN_J_M
28. > rspec spec/sweathr/location_spec.rb Failures: 1) Sweathr::Location#sweater_weather? is time to break out the sweater Failure/Error: expect(weather.sweater_weather?).to be true expected true got false Finished in 0.36974 seconds ( fi les took 0.2812 seconds to load) 1 example, 1 failure 53° F @KEVIN_J_M
29. Direct Interaction ✓ Con fi dence @KEVIN_J_M
30. Direct Interaction ✓ Con fi dence ✓ Production parity @KEVIN_J_M
31. Direct Interaction ✓ Con fi dence ✓ Production parity - Slow @KEVIN_J_M
32. Direct Interaction ✓ Con fi dence ✓ Production parity - Slow - Non-deterministic @KEVIN_J_M
33. Direct Interaction ✓ Con fi dence ✓ Production parity - Slow - Non-deterministic - Dependency required @KEVIN_J_M
34. Direct Interaction ✓ Con fi dence ✓ Production parity - Slow - Non-deterministic - Dependency required - Rate limiting @KEVIN_J_M
35. Why Direct Interaction? ★ Unfamiliar with dependency @KEVIN_J_M
36. Why Direct Interaction? ★ Unfamiliar with dependency ★ Low barrier to interact @KEVIN_J_M
37. Stub
38. before do api_response = { current_observation: { feelslike_f: “55.0” } }.to_json end @KEVIN_J_M
39. before do api_response = { current_observation: { feelslike_f: “55.0” } }.to_json stub_request(:get, url) .to_return(status: 200, body: api_response) end @KEVIN_J_M
40. it "is time to break out the sweater" do location = Sweathr::Location.new( zip_code: “02108") expect(location.sweater_weather?).to be true end @KEVIN_J_M
41. Stub ✓ Deterministic @KEVIN_J_M
42. Stub ✓ Deterministic ✓ Bypass dependency @KEVIN_J_M
43. Stub ✓ Deterministic ✓ Bypass dependency ✓ Isolated unit @KEVIN_J_M
44. Stub ✓ Deterministic ✓ Bypass dependency ✓ Isolated unit - Must know response structure @KEVIN_J_M
45. Stub ✓ Deterministic ✓ Bypass dependency ✓ Isolated unit - Must know response structure - Stub response vs. reality @KEVIN_J_M
46. Stub ✓ Deterministic ✓ Bypass dependency ✓ Isolated unit - Must know response structure - Stub response vs. reality - Possibly verbose @KEVIN_J_M
47. Why Stub? ★ Stable interface @KEVIN_J_M
48. Why Stub? ★ Stable interface ★ Small response @KEVIN_J_M
49. Fake
50. class FakeWeather < Sinatra::Base end @KEVIN_J_M
51. class FakeWeather < Sinatra::Base get “/api/:key/conditions/q/:zip_code.json” do end end @KEVIN_J_M
52. class FakeWeather < Sinatra::Base get “/api/:key/conditions/q/:zip_code.json” do json current_observation: { feelslike_f: "56.0" } end end @KEVIN_J_M
53. it "is time to break out the sweater" do location = Sweathr::Location.new( zip_code: “02108”) end @KEVIN_J_M
54. it "is time to break out the sweater" do location = Sweathr::Location.new( zip_code: “02108”) Capybara::Discoball.spin(FakeWeather) do |s| end end @KEVIN_J_M
55. it "is time to break out the sweater" do location = Sweathr::Location.new( zip_code: “02108”) Capybara::Discoball.spin(FakeWeather) do |s| location.endpoint_url = s.url end end @KEVIN_J_M
56. it "is time to break out the sweater" do location = Sweathr::Location.new( zip_code: “02108”) Capybara::Discoball.spin(FakeWeather) do |s| location.endpoint_url = s.url expect(location.sweater_weather?).to be true end end @KEVIN_J_M
57. Fake ✓ Full stack test @KEVIN_J_M
58. Fake ✓ Full stack test ✓ Local, deployable sandbox @KEVIN_J_M
59. Fake ✓ Full stack test ✓ Local, deployable sandbox ✓ Limited noise in setup @KEVIN_J_M
60. Fake ✓ Full stack test ✓ Local, deployable sandbox ✓ Limited noise in setup ✓ Control fake complexity @KEVIN_J_M
61. Fake ✓ Full stack test ✓ Local, deployable sandbox ✓ Limited noise in setup ✓ Control fake complexity - Maintain consistency @KEVIN_J_M
62. Fake ✓ Full stack test ✓ Local, deployable sandbox ✓ Limited noise in setup ✓ Control fake complexity - Maintain consistency - Test the fake @KEVIN_J_M
63. Why Fake? ★ Need con fi dence in communication @KEVIN_J_M
64. Why Fake? ★ Need con fi dence in communication ★ Multi-step interaction @KEVIN_J_M
65. Fixture
66. it "is time to break out the sweater" do location = Sweathr::Location.new( zip_code: “02108”) end @KEVIN_J_M
67. it "is time to break out the sweater" do location = Sweathr::Location.new( zip_code: “02108”) VCR.use_cassette(“temp_needs_sweater") do end end @KEVIN_J_M
68. it "is time to break out the sweater" do location = Sweathr::Location.new( zip_code: “02108”) VCR.use_cassette(“temp_needs_sweater") do expect(location.sweater_weather?).to be true end end @KEVIN_J_M
69. Fixture ✓ Truth at moment in time @KEVIN_J_M
70. Fixture ✓ Truth at moment in time ✓ Complete picture @KEVIN_J_M
71. Fixture ✓ Truth at moment in time ✓ Complete picture - Mystery guest @KEVIN_J_M
72. Fixture ✓ Truth at moment in time ✓ Complete picture - Mystery guest - Snapshot in time @KEVIN_J_M
73. Fixture ✓ Truth at moment in time ✓ Complete picture - Mystery guest - Snapshot in time - Requires periodic system access @KEVIN_J_M
74. Why Fixture? ★ Need complete response @KEVIN_J_M
75. Why Fixture? ★ Need complete response ★ Dependency accessible @KEVIN_J_M
76. Why Fixture? ★ Need complete response ★ Dependency accessible ★ Fixture creation limits impact on dependency @KEVIN_J_M
77. Why Fixture? ★ Need complete response ★ Dependency accessible ★ Fixture creation limits impact on dependency ★ Can refresh regularly @KEVIN_J_M
78. @KEVIN_J_M STOP
79. @KEVIN_J_M
80. class Location def sweater_weather? uri = URI(conditions_url_for_zip_code) result = Net::HTTP.get(uri) response = JSON.parse(result) feels_like = response.dig( “current_observation”, “feelslike_f”) feels_like.to_f.between?(55, 65) end end @KEVIN_J_M
81. class Location def sweater_weather? uri = URI(conditions_url_for_zip_code) result = Net::HTTP.get(uri) response = JSON.parse(result) feels_like = response.dig( “current_observation”, “feelslike_f”) feels_like.to_f.between?(55, 65) end end 1 @KEVIN_J_M
82. class Location def sweater_weather? uri = URI(conditions_url_for_zip_code) result = Net::HTTP.get(uri) response = JSON.parse(result) feels_like = response.dig( “current_observation”, “feelslike_f”) feels_like.to_f.between?(55, 65) end end 1 2 @KEVIN_J_M
83. class Location def sweater_weather? uri = URI(conditions_url_for_zip_code) result = Net::HTTP.get(uri) response = JSON.parse(result) feels_like = response.dig( “current_observation”, “feelslike_f”) feels_like.to_f.between?(55, 65) end end 1 2 3 @KEVIN_J_M
84. API Client
85. module Sweathr module Weather class Api end end end @KEVIN_J_M
86. module Sweathr module Weather class Api def current_conditions(zip:) end end end end @KEVIN_J_M
87. module Sweathr module Weather class Api def current_conditions(zip:) uri = URI( “#{auth_uri}/conditions/q/#{zip}.json”) end end end end @KEVIN_J_M
88. module Sweathr module Weather class Api def current_conditions(zip:) uri = URI( “#{auth_uri}/conditions/q/#{zip}.json”) JSON.parse(Net::HTTP.get(uri)) end end end end @KEVIN_J_M
89. it "retrieves the current conditions" do VCR.use_cassette("temp_needs_sweater") do end end @KEVIN_J_M
90. it "retrieves the current conditions" do VCR.use_cassette("temp_needs_sweater") do result = api.current_conditions(zip: “02108") end end @KEVIN_J_M
91. it "retrieves the current conditions" do VCR.use_cassette("temp_needs_sweater") do result = api.current_conditions(zip: “02108") expect(result).to include( "current_observation" => a_hash_including( "feelslike_f" => a_kind_of(String) ) ) end end @KEVIN_J_M
92. Data Representation
93. module Sweathr module Weather class CurrentConditions end end end @KEVIN_J_M
94. module Sweathr module Weather class CurrentConditions def initialize(results) @results = results end end end end @KEVIN_J_M
95. module Sweathr module Weather class CurrentConditions def initialize(results) @results = results end def feels_like_f end end end end @KEVIN_J_M
96. module Sweathr module Weather class CurrentConditions def initialize(results) @results = results end def feels_like_f value = @results.dig( "current_observation", “feelslike_f") end end end end @KEVIN_J_M
97. module Sweathr module Weather class CurrentConditions def initialize(results) @results = results end def feels_like_f value = @results.dig( "current_observation", “feelslike_f") string_to_ fl oat(value) end end end end @KEVIN_J_M
98. describe "#feels_like_f" do it “gives the feels like temp in Fahrenheit" do end end @KEVIN_J_M
99. describe "#feels_like_f" do it “gives the feels like temp in Fahrenheit" do conditions = Sweathr::Weather::CurrentConditions .new(json) end end @KEVIN_J_M
100. describe "#feels_like_f" do it “gives the feels like temp in Fahrenheit" do conditions = Sweathr::Weather::CurrentConditions .new(json) expect(conditions.feels_like_f).to eq 55.5 end end @KEVIN_J_M
101. describe "#feels_like_f" do it “gives the feels like temp in Fahrenheit" do conditions = Sweathr::Weather::CurrentConditions .new(json) expect(conditions.feels_like_f).to eq 55.5 end context "with a non-numeric result";end end @KEVIN_J_M
102. describe "#feels_like_f" do it “gives the feels like temp in Fahrenheit" do conditions = Sweathr::Weather::CurrentConditions .new(json) expect(conditions.feels_like_f).to eq 55.5 end context "with a non-numeric result";end context "with no current observation”;end end @KEVIN_J_M
103. describe "#feels_like_f" do it "gives the feels like temp in Fahrenheit” do conditions = Sweathr::Weather::CurrentConditions .new(json) expect(conditions.feels_like_f).to eq 55.5 end context "with a non-numeric result";end context "with no current observation”;end context "with no feels like f temperature";end end @KEVIN_J_M
104. Domain
105. module Sweathr module Weather end end @KEVIN_J_M
106. module Sweathr module Weather def self.client @client ||= Api.new end end end @KEVIN_J_M
107. module Sweathr module Weather def self.client @client ||= Api.new end def self.current_conditions(zip_code:) end end end @KEVIN_J_M
108. module Sweathr module Weather def self.client @client ||= Api.new end def self.current_conditions(zip_code:) Sweathr::Weather::CurrentConditions.new( client.current_conditions(zip: zip_code)) end end end @KEVIN_J_M
109. Implementation
110. class Location def sweater_weather? end end @KEVIN_J_M
111. class Location def sweater_weather? current = Sweathr::Weather.current_conditions( zip_code: @zip_code) end end @KEVIN_J_M
112. class Location def sweater_weather? current = Sweathr::Weather.current_conditions( zip_code: @zip_code) current.feels_like_f.between?(55, 65) end end @KEVIN_J_M
113. module Sweathr module Weather def self.client @client ||= Api.new end end end @KEVIN_J_M
114. module Sweathr module Weather def self.client @client ||= Api.new end def self.client=(client) end end end @KEVIN_J_M
115. module Sweathr module Weather def self.client @client ||= Api.new end def self.client=(client) @client = client end end end @KEVIN_J_M
116. Fake Client
117. class FakeWeatherClient end @KEVIN_J_M
118. class FakeWeatherClient def current_conditions(zip:) end end @KEVIN_J_M
119. class FakeWeatherClient def current_conditions(zip:) { "current_observation" => { "feelslike_f" => @results[zip_code] } } end end @KEVIN_J_M
120. class FakeWeatherClient def current_conditions(zip:) { "current_observation" => { "feelslike_f" => @results[zip_code] } } end def add_condition(zip_code:, temp_f:) end end @KEVIN_J_M
121. class FakeWeatherClient def current_conditions(zip:) { "current_observation" => { "feelslike_f" => @results[zip_code] } } end def add_condition(zip_code:, temp_f:) @results[zip_code] = temp_f end end @KEVIN_J_M
122. Test Mode
123. module Sweathr module Testing end end @KEVIN_J_M
124. module Sweathr module Testing def self.enable! end end end @KEVIN_J_M
125. module Sweathr module Testing def self.enable! Sweathr::Weather.client = FakeWeatherClient.new end end end @KEVIN_J_M
126. module Sweathr module Testing def self.enable! Sweathr::Weather.client = FakeWeatherClient.new end def self.disable! end end end @KEVIN_J_M
127. module Sweathr module Testing def self.enable! Sweathr::Weather.client = FakeWeatherClient.new end def self.disable! Sweathr::Weather.client = Sweathr::Weather::Api.new end end end @KEVIN_J_M
128. Testing
129. it "is time to break out the sweater" do end @KEVIN_J_M
130. it "is time to break out the sweater" do Sweathr::Testing.enable! end @KEVIN_J_M
131. it "is time to break out the sweater" do Sweathr::Testing.enable! Sweathr::Weather.client.add_condition( zip_code: "02108", temp_f: “56.0") end @KEVIN_J_M
132. it "is time to break out the sweater" do Sweathr::Testing.enable! Sweathr::Weather.client.add_condition( zip_code: "02108", temp_f: “56.0") location = Sweathr::Location.new( zip_code: “02108”) end @KEVIN_J_M
133. it "is time to break out the sweater" do Sweathr::Testing.enable! Sweathr::Weather.client.add_condition( zip_code: "02108", temp_f: “56.0") location = Sweathr::Location.new( zip_code: “02108”) expect(location.sweater_weather?).to be true end @KEVIN_J_M
134. it "is time to break out the sweater" do Sweathr::Testing.enable! Sweathr::Weather.client.add_condition( zip_code: "02108", temp_f: “56.0") location = Sweathr::Location.new( zip_code: “02108”) expect(location.sweater_weather?).to be true Sweathr::Testing.disable! end @KEVIN_J_M
135. Test Mode ✓ Speed @KEVIN_J_M
136. Test Mode ✓ Speed ✓ State control @KEVIN_J_M
137. Test Mode ✓ Speed ✓ State control ✓ Metadata tracking @KEVIN_J_M
138. Test Mode ✓ Speed ✓ State control ✓ Metadata tracking - No dependency interaction @KEVIN_J_M
139. Test Mode ✓ Speed ✓ State control ✓ Metadata tracking - No dependency interaction - Test mode vs. reality @KEVIN_J_M
140. Why Test Mode? ★ Have dependency coverage elsewhere @KEVIN_J_M
141. Why Test Mode? ★ Have dependency coverage elsewhere ★ Need interaction with results @KEVIN_J_M
142. Testing Third-Party Dependencies? @KEVIN_J_M
143. DON’T* @KEVIN_J_M
144. @KEVIN_J_M
145. Client @KEVIN_J_M
146. Client Data @KEVIN_J_M
147. Client Data Domain @KEVIN_J_M
148. Client Data Domain @KEVIN_J_M
149. Client Data Domain @KEVIN_J_M
150. Client Data Domain @KEVIN_J_M
151. Client Data Domain @KEVIN_J_M
152. @KEVIN_J_M
153. Limit Interaction @KEVIN_J_M
154. Limit Interaction Test Con fi dently @KEVIN_J_M
155. Gnar Company Logo https://github.com/kevin-j-m/testing-services @KEVIN_J_M https://thegnar.co