SOLID and TDD, Sitting in a Tree

Watch it online: http://confreaks.com/videos/2653-rockymountainruby2013-solid-and-tdd-sitting-in-a-tree

You’ve heard the claims or know from experience that test-driven development (TDD) produces better code. Perhaps you’ve also heard that to write better code you should be following the SOLID principles. Is there a connection between practicing TDD and writing SOLID code?

In this talk, I’ll use examples gleaned from real life to demonstrate how TDD prompts us to produce code that conforms to the SOLID principles, and how the SOLID principles are where we should turn when our tests are causing us pain. In doing so, we’ll learn what each principle really means and why it’s valuable.

Mike Nicholaides has been a Rails consultant since 2006 and has always obsessed about writing clean, clear, and concise code. He organizes the Code Retreat in Philadelphia where the focus is on learning TDD, communicating with code, and of course, having fun.

Presented by Mike Nicholaides at Rocky Mountain Ruby Conf. https://www.promptworks.com

Transcript

1. TDD & SOLID Mike Nicholaides
2. http://promptworks.com! @promptworks
3. describe Notifier, "#notify" do let(:message_body) do "Hi @#{notifiable_user1.name} @#{notifiable_user2.name}\ @#{ unnotifiable_user.name }" end ! let(:message) { create(:message, body: message_body) } ! it "FB's the message's mentioned users who prefer to be FB'd" do notifiable_user1 = create(:facebook_connected_user, fb_me_on_mention: true) notifiable_user2 = create(:facebook_connected_user, fb_me_on_mention: true) unnotifiable_user = create(:facebook_connected_user, fb_me_on_mention: false) ! notifiable_user1.facebook_connection.stub(put_connections: true) notifiable_user2.facebook_connection.stub(put_connections: true) unnotifiable_user.facebook_connection.stub(put_connections: true) ! Notifier.notify(message) ! expected_message = "#{message.author.name} said #{message_body}" ! expect(notifiable_user1.facebook_connection).to have_received(:put_connections).with("me", "feed", message: expected_message) expect(notifiable_user2.facebook_connection).to have_received(:put_connections).with("me", "feed", message: expected_message) expect(unnotifiable_user.facebook_connection).not_to have_received(:put_connections) end ! it "emails the message's mentioned users who prefer to be emailed" do notifiable_user1 = create(:user, email_me_on_mention: true) notifiable_user2 = create(:user, email_me_on_mention: true) unnotifiable_user = create(:user, email_me_on_mention: false) ! MessageMailer.stub(:deliver_message) ! Notifier.notify(message) ! expected(MessageMailer).to have_received(:deliver_message).with(message, [notifiable_user1, notifiable_user2]) end ! it "SMS's the message's mentioned users who prefer to be SMS'd" do notifiable_user1 = create(:sms_user, sms_me_on_mention: true) notifiable_user2 = create(:sms_user, sms_me_on_mention: true) unnotifiable_user = create(:sms_user, sms_me_on_mention: false) ! SMSGateway.stub(:deliver) ! Notifier.notify(message) ! expected_message = "#{message.author.name} said #{message_body}" ! expect(SMSGateway).to have_received(:deliver).with(expected_message, notifiable_user1.sms_number) expect(SMSGateway).to have_received(:deliver).with(expected_message, notifiable_user2.sms_number) end end
4. class Notifier def self.notify(message) message.mentioned_users. select(&:fb_me_on_mention?). select(&:facebook_connection). each do |user| user.facebook_connection.put_connections( "me", "feed", message: "#{message.author.name} said: #{message.body}" ) end ! email_users = message.mentioned_users. select(&:email_me_on_mention?). select{|u| u.email.present? } MessageMailer.deliver_message(message, email_users) ! message.mentioned_users. select(&:sms_me_on_mention?). select{|u| u.sms_number.present? }. each { |user| SMSGateway.deliver(message, user.sms_number) } end end
5. Test first != good code
6. SOLID
7. Interface Segregation Principle “many client-specific interfaces are better than one general-purpose interface.” ! Robert C. Martin Principles of Object Oriented Design
8. Dependency Inversion Principle “Depend upon abstractions. Do not depend upon concretions.” ! ! Robert C. Martin, Design Principles and Design Patterns
9. Depending on a Concretion def save_my_game if game_changed? File.open('game.txt', 'w') do |file| file.print @game_data end end end ! save_my_game
10. Depending on an Abstraction def save_my_game persistent_store = FileStore.new persistent_store.save(@game_data) if game_changed? end ! save_my_game class FileStore def save(game_data) File.open('game.txt', 'w') do |file| file.print game_data end end end
11. Dependency Inversion Principle hide concretions behind abstractions
12. Open/Closed Principle “Software entities … should be open for extension, but closed for modification” ! Bertrand Meyer, Object Oriented Software Construction
13. Open/Closed Principle • dependencies • collaborators • logic Swappable pieces for
14. Open/Closed Principle • blocks • inheritance • dependency injection Techniques
15. Open/Closed Principle def save_my_game(persistent_store) persistent_store.save(@game_data) if game_changed? end ! save_my_game(FileStore.new)
16. Open/Closed Principle Make entities extendible
17. Liskov Substitution Principle • use duck typing
18. Liskov Substitution Principle def save_my_game(persistent_store) persistent_store.save(@game_data) if game_changed? end
19. Single Responsibility Principle “A class should have one, and only one, reason to change.” ! Robert C. Martin Principles of Object Oriented Design
20. Single Responsibility Principle • classes should be small • classes should do one thing • we should have lots of classes
21. SOLID • hide concretions behind abstractions • make entities extendible • use duck typing • classes should do one thing
22. message.author # => User @JesseKatsopolis ! message.body # => "@DannyTanner, @JoeyGladstone, Watch the hair!" ! message.mentioned_users # => [ User @DannyTanner, User @JoeyGladstone ]
23. # ... ! if @message.save ! Notifier.notify(@message) ! redirect_to @message else ! # ...
24. describe Notifier, ".notify" do ! it "emails the message's mentioned users who prefer to be emailed" it "SMS's the message's mentioned users who prefer to be SMS'd" it "FB's the message's mentioned users who prefer to be FB'd" ! end
25. Details • what it does • what is knows
26. Responsibilities • email users • SMS users • FB users ! Concretions • the message • the mentioned users • how to determine if someone wants to be emailed • how to determine if someone wants to be SMS'd • how to determine if someone wants to be FB'd

27. Responsibilities Described it "emails the message's mentioned users who prefer to be emailed" it "SMS's the message's mentioned users who prefer to be SMS'd" it "FB's the message's mentioned users who prefer to be FB'd"
28. Strained Language It emails the messages' mentioned users who prefer to be emailed.
29. it "FB's the message's mentioned users who prefer to be FB'd" do ! notifiable_user1 = create(:facebook_connected_user, fb_me_on_mention: true) notifiable_user2 = create(:facebook_connected_user, fb_me_on_mention: true) unnotifiable_user = create(:facebook_connected_user, fb_me_on_mention: false) ! message_body = "Hi @#{notifiable_user1.name} @#{notifiable_user2.name}\ @#{ unnotifiable_user.name }" ! message = create(:message, body: message_body) ! notifiable_user1.facebook_connection.stub(put_connections: true) notifiable_user2.facebook_connection.stub(put_connections: true) unnotifiable_user.facebook_connection.stub(put_connections: true) ! Notifier.notify(message) ! expected_message = "#{message.author.name} said #{message_body}" ! expect(notifiable_user1.facebook_connection). to have_received(:put_connections). with("me", "feed", message: expected_message) ! expect(notifiable_user2.facebook_connection). to have_received(:put_connections). with("me", "feed", message: expected_message) ! expect(unnotifiable_user.facebook_connection). not_to have_received(:put_connections) ! end
30. too many details == hard to test
31. describe Notifier, "#notify" do let(:message_body) do "Hi @#{notifiable_user1.name} @#{notifiable_user2.name}\ @#{ unnotifiable_user.name }" end ! let(:message) { create(:message, body: message_body) } ! it "FB's the message's mentioned users who prefer to be FB'd" do notifiable_user1 = create(:facebook_connected_user, fb_me_on_mention: true) notifiable_user2 = create(:facebook_connected_user, fb_me_on_mention: true) unnotifiable_user = create(:facebook_connected_user, fb_me_on_mention: false) ! notifiable_user1.facebook_connection.stub(put_connections: true) notifiable_user2.facebook_connection.stub(put_connections: true) unnotifiable_user.facebook_connection.stub(put_connections: true) ! Notifier.notify(message) ! expected_message = "#{message.author.name} said #{message_body}" ! expect(notifiable_user1.facebook_connection).to have_received(:put_connections).with("me", "feed", message: expected_message) expect(notifiable_user2.facebook_connection).to have_received(:put_connections).with("me", "feed", message: expected_message) expect(unnotifiable_user.facebook_connection).not_to have_received(:put_connections) end ! it "emails the message's mentioned users who prefer to be emailed" do notifiable_user1 = create(:user, email_me_on_mention: true) notifiable_user2 = create(:user, email_me_on_mention: true) unnotifiable_user = create(:user, email_me_on_mention: false) ! MessageMailer.stub(:deliver_message) ! Notifier.notify(message) ! expected(MessageMailer).to have_received(:deliver_message).with(message, [notifiable_user1, notifiable_user2]) end ! it "SMS's the message's mentioned users who prefer to be SMS'd" do notifiable_user1 = create(:sms_user, sms_me_on_mention: true) notifiable_user2 = create(:sms_user, sms_me_on_mention: true) unnotifiable_user = create(:sms_user, sms_me_on_mention: false) ! SMSGateway.stub(:deliver) ! Notifier.notify(message) ! expected_message = "#{message.author.name} said #{message_body}" ! expect(SMSGateway).to have_received(:deliver).with(expected_message, notifiable_user1.sms_number) expect(SMSGateway).to have_received(:deliver).with(expected_message, notifiable_user2.sms_number) end end
32. class Notifier def self.notify(message) message.mentioned_users. select(&:fb_me_on_mention?). select(&:facebook_connection). each do |user| user.facebook_connection.put_connections( "me", "feed", message: "#{message.author.name} said: #{message.body}" ) end ! email_users = message.mentioned_users. select(&:email_me_on_mention?). select{|u| u.email.present? } MessageMailer.deliver_message(message, email_users) ! message.mentioned_users. select(&:sms_me_on_mention?). select{|u| u.sms_number.present? }. each { |user| SMSGateway.deliver(message, user.sms_number) } end end
33. Guidelines for Pain-Free Testing ! • defer responsibilities to other classes • assume good abstractions
34. it "emails the message's mentioned users who prefer to be emailed" it "SMS's the message's mentioned users who prefer to be SMS'd" it "FB's the message's mentioned users who prefer to be FB'd"
35. it "______ the message's mentioned users who prefer to be ______" it "______ the message's mentioned users who prefer to be ______" it "______ the message's mentioned users who prefer to be ______"
36. it "______ the message's mentioned users who prefer to be ______"
37. it "notifies via SMS/FB/Email the message's mentioned users who prefer to be notified via SMS/FB/Email, respectively"
38. it "notifies the message's mentioned users via their preferred notification channels"
39. it "notifies the message's mentioned users via notification channels"
40. it "notifies mentioned users via notification channels"
41. it "notifies mentioned users via notification channels" do ! message = double('message') channels = [ double(notify_about_message: nil), double(notify_about_message: nil) ] notifier = Notifier.new(channels) ! notifier.notify(message) ! channel[0].should have_received(:notify_about_message).with message channel[1].should have_received(:notify_about_message).with message ! end
42. class Notifier ! def initialize(channels) @channels = channels end ! def notify(message) @channels.each do |channel| channel.notify_about_message(message) end end ! end ! notifier = Notifier.new(channels) notifier.notify(message)
43. channels = case Rails.env when 'production' [ EmailChannel.new, SMSChannel.new, NSAChannel.new ] when 'staging' [ TestEmailChannel.new, TestSMSChannel.new ] else [ LoggingChannel.new ] end ! config.notifier = Notifier.new( channels )
44. it "emails the message's mentioned users who prefer email" do ! message = build(:message, mentioned_users: [ user_who_likes_email1 = build(:user, email_on_mention: true), user_who_likes_email2 = build(:user, email_on_mention: true), user_who_dislikes_email = build(:user, email_on_mention: false) ]) MessageMailer.stub(:deliver_message) ! EmailChannel.new.notify(message) ! MessageMailer.should have_received(:deliver_message) .with(message, [user_who_likes_email1, user_who_likes_email2]) ! end
45. - notify via channels Notifier - how to notify by email - who prefers to be emailed Email Channel - how to notify by SMS - who prefers to be SMS'd SMS Channel - who prefers to be Facebooked - how to notify by Facebook Facebook Channel - which channels < Configuration > - which users are mentioned Message - email address - Facebook Credentials - SMS number User - notify by email - notify by SMS - notify by Facebook - how to notify by email - who prefers to be emailed - how to notify by SMS - who prefers to be SMS'd - who prefers to be Facebooked - how to notify by Facebook Notifier - which users are mentioned Message - email address - Facebook Credentials - SMS number User
46. @nicholaides mike@promptworks.com