Testing Magic

An overview of the concepts behind TDD, complete with a run through the much more practical Sandi Metz rules of testing.

It aims at giving you the building blocks to do TDD and actually enjoy it.

Transcript

1. Testing Magic by Luís Zamith
2. @zamith
4. Test Driven Development A guy called Kent Beck came up with a different way of writing code, and called it
6. it takes too much TIME
7. it takes too much TIME need to get SH*T DONE
8. it takes too much TIME need to get SH*T DONE tests are EXPENSIVE
9. Productivity Time w/o tests with tests *completely fictional data
10. Fixing bugs over and over again Large classes and methods Code is a mess Fear of change Hard to refactor
11. Fixing bugs over and over again Large classes and methods Code is a mess Fear of change Hard to refactor these are symptoms of bad practices
12. TDD is NOT the cure!
13. TDD is NOT the cure! But it sure helps...
14. RED GREEN REFACTOR
15. RED GREEN REFACTOR do the smallest step you can
16. RED GREEN REFACTOR stay here as little as possible do the smallest step you can
17. RED GREEN REFACTOR stay here as little as possible do the smallest step you can go drink a beer
18. - More focused classes - Looser coupling - Cleaner interfaces - More confidence in your code you get: you don’t get: - Bug free code - The best code in the world
19. Not allowed to write: - code unless it is to make a test pass - more of a test than is sufficient to fail - more code than is sufficient to pass the test BOB MARTIN picture source: http://agile2012.agilealliance.org
20. It’s your job as a developer to write your own tests.
21. There is more to testing than TDD, go check it out so you can chose your way...
22. magic tricks of testing Testing is hard, and when you make a change that breaks half your tests you feel you’ve been wasting your time. Well, fear not young chap, and come learn some
23. I hate my tests
24. I hate my tests Why do ?
26. They are slow
27. They are slow They are expensive
28. They are slow They are expensive They are fragile
29. They are slow They are expensive They are fragile
30. Your app is still a mess
31. THAT CAN CHANGE YOUR LIFE CAN BE SAVED!
32. OOP focuses on messages A B
33. Message origin SUT Sent to self Incoming Outgoing
34. Message type Query A B return something change nothing Command A B return nothing change something
35. What about methods that do both?
36. What about methods that do both? Separate them into two. SRP, remember?
37. Query Command Incoming Sent to self Outgoing Message type Message origin
38. Incoming Query Messages
39. class Player < Struct.new :height, :weight def body_mass_index (weight / height**2).round 1 end end object
40. class Player < Struct.new :height, :weight def body_mass_index (weight / height**2).round 1 end end describe Player do context "#body_mass_index" do it "calculates the bmi" do lebron = Player.new 2.03, 113 lebron.body_mass_index.should eq 27.4 end end end object test
41. ASSERTIONS Test incoming query messages by making about what they SEND BACK
42. Query Command Incoming Sent to self Outgoing Message type Message origin
43. Query Command Incoming Sent to self Outgoing Message type Message origin Assert result
44. WARNING Test the interface not the implementation
45. Incoming Command Messages
46. class Player < Struct.new :height, :weight attr_reader :skill def skill=(skill_level) @skill = skill_level end end object
47. class Player < Struct.new :height, :weight attr_reader :skill def skill=(skill_level) @skill = skill_level end end describe Player do context "#skill=" do it "updates the skill level" do player.skill = 10 player.skill.should eq 10 end end end object test
48. ASSERTIONS Test incoming command messages by making about DIRECT PUBLIC SIDE EFFECTS
49. Query Command Incoming Sent to self Outgoing Message type Message origin Assert result
50. Query Command Incoming Sent to self Outgoing Message type Message origin Assert result Assert direct public side effects
51. Sent to self Messages
52. object class Player < Struct.new :height, :weight def body_mass_index actual_bmi.round 1 end private def actual_bmi (weight / height**2) end end
53. object class Player < Struct.new :height, :weight def body_mass_index actual_bmi.round 1 end private def actual_bmi (weight / height**2) end end
54. object class Player < Struct.new :height, :weight def body_mass_index actual_bmi.round 1 end private def actual_bmi (weight / height**2) end end
55. object class Player < Struct.new :height, :weight def body_mass_index actual_bmi.round 1 end private def actual_bmi (weight / height**2) end end testing state is redundant
56. describe Player do context "#body_mass_index" do it "calculates the bmi" do lebron = Player.new 2.03, 113 lebron.should_receive(:actual_bmi).and_call_original lebron.body_mass_index.should eq 27.4 end end end test
57. describe Player do context "#body_mass_index" do it "calculates the bmi" do lebron = Player.new 2.03, 113 lebron.should_receive(:actual_bmi).and_call_original lebron.body_mass_index.should eq 27.4 end end end test Over specification: no safety and breaks on every change
58. Do not test private methods RULE
59. Do not test private methods RULE Break at your own risk if it saves $$ in development
60. Query Command Incoming Sent to self Outgoing Message type Message origin Assert result Assert direct public side effects
61. Query Command Incoming Sent to self Outgoing Message type Message origin Assert result Assert direct public side effects Ignore
62. Outgoing Query Messages
63. object class Player < Struct.new :height, :weight def on_the_team?(team) team.has_player? self end end
64. object class Player < Struct.new :height, :weight def on_the_team?(team) team.has_player? self end end Player on_the_team? has_player? outgoing incoming Team
65. test describe Player do context "#on_the_team?" do it "finds if player is on the team" do team = Team.new team.add_player player player.should be_on_the_team team team.players.should include player end end end
66. test Redundant: duplicates team’s tests describe Player do context "#on_the_team?" do it "finds if player is on the team" do team = Team.new team.add_player player player.should be_on_the_team team team.players.should include player end end end
67. test describe Player do context "#on_the_team?" do it "finds if player is on the team" do team = Team.new team.add_player player team.should_receive (:has_player?).and_call_original player.should be_on_the_team team end end end
68. test Over specification: adds costs and no benefits describe Player do context "#on_the_team?" do it "finds if player is on the team" do team = Team.new team.add_player player team.should_receive (:has_player?).and_call_original player.should be_on_the_team team end end end
69. Do not test outgoing query messages RULE
70. Do not test outgoing query messages RULE If the message has no visible side effects the sender should not test it
71. Query Command Incoming Sent to self Outgoing Message type Message origin Assert result Assert direct public side effects Ignore
72. Query Command Incoming Sent to self Outgoing Message type Message origin Assert result Assert direct public side effects Ignore
73. Outgoing Command Messages
74. object class Player < Struct.new :height, :weight def infiltrate_team(team) team.add_player self end end
75. object class Player < Struct.new :height, :weight def infiltrate_team(team) team.add_player self end end describe Player do context "#infiltrate_team" do it "adds player to team" do team = Team.new player.infiltrate_team team team.players.should include player end end end test
76. object class Player < Struct.new :height, :weight def infiltrate_team(team) team.add_player self end end describe Player do context "#infiltrate_team" do it "adds player to team" do team = Team.new player.infiltrate_team team team.players.should include player end end end test depends on distant side effect
77. object class Player < Struct.new :height, :weight def infiltrate_team(team) team.add_player self end end describe Player do context "#infiltrate_team" do it "adds player to team" do team = Team.new player.infiltrate_team team team.players.should include player end end end test not the player’s responsibility
78. object class Player < Struct.new :height, :weight def infiltrate_team(team) team.add_player self end end
79. object class Player < Struct.new :height, :weight def infiltrate_team(team) team.add_player self end end this message must be sent
80. object class Player < Struct.new :height, :weight def infiltrate_team(team) team.add_player self end end describe Player do context "#infiltrate_team" do it "adds player to team" do team = Team.new team.should_receive(:add_player) player.infiltrate_team team end end end test this message must be sent
81. object class Player < Struct.new :height, :weight def infiltrate_team(team) team.add_player self end end describe Player do context "#infiltrate_team" do it "adds player to team" do team = Team.new team.should_receive(:add_player) player.infiltrate_team team end end end test this message must be sent depends on the interface
82. it’s the player responsibility to send add_player to the team object class Player < Struct.new :height, :weight def infiltrate_team(team) team.add_player self end end describe Player do context "#infiltrate_team" do it "adds player to team" do team = Team.new team.should_receive(:add_player) player.infiltrate_team team end end end test this message must be sent
83. EXPECT outgoing command messages to send
84. EXPECT outgoing command messages to send if side effects are stable and cheap, rule might be broken
85. Query Command Incoming Sent to self Outgoing Message type Message origin Assert result Assert direct public side effects Ignore
86. Query Command Incoming Sent to self Outgoing Message type Message origin Assert result Assert direct public side effects Ignore Expect to send
87. Ensure mocks are in sync with public API RULE
88. - Test everything, but only once - Test the interfaces - Trust collaborators - In doubt, go for simple SUMMARY
89. Thanks.
90. - https://speakerdeck.com/skmetz/magic-tricks-of-testing- railsconf?slide=0 - http://butunclebob.com/ ArticleS.UncleBob.TheThreeRulesOfTdd - http://blog.zamith.pt/blog/2013/04/10/understanding-the- heart-to-become-a-better-doctor/ - http://www.amazon.com/Clean-Code-Handbook-Software- Craftsmanship/dp/0132350882?tag=viglink127254-20 - http://www.amazon.com/dp/0321721330 - http://www.cleancoders.com - https://learn.thoughtbot.com/purchases/ d27fb3e007037d4ef543caf84d87ecc7 - http://www.amazon.com/RSpec-Book-Behaviour- Development-Cucumber/dp/1934356379 We stand on the shoulders of giants - http://www.amazon.com/Test-Driven- Development-By-Example/dp/0321146530? tag=giantrobotssm-20 - https://peepcode.com/products/rspec-i - https://peepcode.com/products/rspec-ii - http://robots.thoughtbot.com/post/23112388518/ types-of-coupling
91. Luís Zamith @zamith blog.zamith.pt