SOLID Principles through tests

A practical approach on how to integrating the SOLID principles to the way we write code will pay off in the long the term.

Presented at: RubyConf Brazil 2014

1. SOLID Principles Through Tests
2. @sebasoga Sebastián Sogamoso
5. Kung-fu
6. Shaolin Kungfu
7. The most well known principle is called Six Harmonies
8. Three External Harmonies
9. Three Internal Harmonies
10. We all follow some sort of principle
11. SOLID Principles Through Tests
12. Set of 5 object design level principles
14. S O L I D
15. Prevent our systems from rotting
16. Code that will save us time and money
17. Cats follow the 6 harmonies to practice Kungfu We should follow principles when writing code RECAP
18. Story Time
19. Some facts of this story are true and some are made up
20. We’ll call him Steven Seagull
21. E-commerce system • Initial status: supports a few shipping methods • Requirement: painlessly add new shipping methods as needed
22. class Order ... def ship case @store.shipping_method when Shipping::RegularMethod @store.shipping_method.pack(@items, @buyer, @seller).ship when Shipping::OvernightMethod origin = @seller.address destination = “#{@buyer.address_line1}, #{@buyer.zip}" @store.shipping_method.ship_order(origin, destination, @items) when Shipping::SameDayMethod addresses = [@seller.address, @buyer.complete_address] @store.shipping_method.pack(@items, addresses).send end end ... end
23. def ship case @store.shipping_method when Shipping::RegularMethod @store.shipping_method.pack(@items, @buyer, @seller).ship when Shipping::OvernightMethod origin = @seller.address destination = “#{@buyer.address_line1}, #{@buyer.zip}" @store.shipping_method.ship_order(origin, destination, @items) when Shipping::SameDayMethod addresses = [@seller.address, @buyer.complete_address] @store.shipping_method.pack(@items, addresses).send when Shipping::NewMethod ... end end
24. Shotgun surgery
25. class Order ... def ship(shipping_method) case shipping_method when Shipping::RegularMethod shipping_method.pack(@items, @buyer, @seller).ship when Shipping::OvernightMethod origin = @seller.address destination = “#{@buyer.address_line1}, #{@buyer.zip}" shipping_method.ship_order(origin, destination, @items) when Shipping::SameDayMethod addresses = [@seller.address, @buyer.complete_address] @store.shipping_method.pack(@items, addresses).send else shipping_method.ship_order(self) end end ... end
26. We were able to extend a class behavior, without modifying it RECAP
27. S O L I D Open Closed
28. class Order ... def ship(shipping_method) case shipping_method when Shipping::RegularMethod shipping_method.ship_order(self) when Shipping::OvernightMethod shipping_method.ship_order(self) when Shipping::SameDayMethod shipping_method.ship_order(self) else shipping_method.ship_order(self) end end ... end
29. .................................. .................................. ....................... Finished in 129600.024296s 91 examples, 21 failures, 0 skips
30. describe Order do describe "#ship" do ... subject { Order.new } context "when shipping method is a Shipping::RegularMethod" do it "uses Shipping::RegularMethod to ship the order" do allow(shipping_method).to receive(class: Shipping::RegularMethod) subject.ship expect(shipping_method). to have_received_message_chain(:pack, :ship). with(items, seller, buyer) end end context "when shipping method is a Shipping::OvernightMethod" do it "uses Shipping::OvernightMethod to ship the order" do allow(shipping_method).to receive(class: Shipping::OvernightMethod) subject.ship expect(shipping_method). to have_received(:ship_order) end end context "when shipping method is a Shipping::SameDayMethod" do it "uses Shipping::SameDayMethod to ship the order" do allow(shipping_method).to receive(class: Shipping::SameDayMethod) subject.ship expect(shipping_method). to have_received_message_chain(:pack, :send). end end end end
31. context "when shipping method is a Shipping::OvernightMethod" do it "uses Shipping::OvernightMethod to ship the order" do allow(shipping_method).to receive(class: Shipping::OvernightMethod) subject.ship expect(shipping_method). to have_received(:ship_order) end end
32. Listen to your tests
33. Tests are the first client of the system
34. “TDD doesn’t drive good design. TDD gives you immediate feedback about what’s likely to be bad design” Kent Beck
35. Order Shipping method
36. Concrete things change a lot, abstract things change much less frequently
37. class Order ... def ship(shipping_method) case shipping_method when Shipping::RegularMethod shipping_method.pack(@items, @buyer, @seller).ship when Shipping::OvernightMethod origin = @seller.address destination = “#{@buyer.address_line1}, #{@buyer.zip}" shipping_method.ship_order(origin, destination, @items) when Shipping::SameDayMethod addresses = [@seller.address, @buyer.complete_address] @store.shipping_method.pack(@items, addresses).send else shipping_method.ship_order(self) end end ... end
38. module Shipping class RegularMethod < BaseMethod ... def self.ship_order(order) new. pack(order.items, order.origin, order.destination) .ship end ... end end
39. class Order ... def ship(shipping_method) case shipping_method when Shipping::RegularMethod shipping_method.ship_order(self) when Shipping::OvernightMethod origin = @seller.address destination = “#{@buyer.address_line1}, #{@buyer.zip}" shipping_method.ship_order(origin, destination, @items) when Shipping::SameDayMethod addresses = [@seller.address, @buyer.complete_address] @store.shipping_method.pack(@items, addresses).send else shipping_method.ship_order(self) end end ... end
40. class Order ... def ship(shipping_method) case shipping_method when Shipping::OvernightMethod origin = @seller.address destination = “#{@buyer.address_line1}, #{@buyer.zip}" shipping_method.ship_order(origin, destination, @items) when Shipping::SameDayMethod addresses = [@seller.address, @buyer.complete_address] @store.shipping_method.pack(@items, addresses).send else shipping_method.ship_order(self) end end ... end
41. describe Order do describe "#ship" do ... subject { Order.new } context "when shipping method is a Shipping::OvernightMethod" do it “ships the order using the given shipping method" do order = Order.new allow(shipping_method).to receive(class: Shipping::OvernightMethod) allow(shipping_method).to receive(:ship_order) { ‘ordered shipped’ } expect(order.ship(shipping_method).to eq ‘ordered shipped’ end end context "when shipping method is a Shipping::SameDayMethod" do it “ships the order using the given shipping method" do order = Order.new allow(shipping_method).to receive(class: Shipping::SameDayMethod) allow(shipping_method).to receive(:ship_order) { ‘ordered shipped’ } expect(order.ship(shipping_method).to eq ‘ordered shipped’ end end context "when shipping method is a different type" do it "uses Shipping::SameDayMethod to ship the order" do allow(shipping_method).to receive(class: nil) subject.ship expect(shipping_method). to have_received_message_chain(:pack, :send). end end end end
42. describe Order do ... describe "#ship" do let(:shipping_method) { double(:shipping_method) } subject { Order.new } it “ships the order using the given shipping method" do order = Order.new.pack allow(shipping_method).to receive(:ship_order) { ‘ordered shipped’ } expect(order.ship(shipping_method).to eq ‘ordered shipped’ end ... end
43. class Order ... def ship(shipping_method) case shipping_method.class when Shipping::RegularMethod shipping_method.ship_order(self) when Shipping::OvernightMethod shipping_method.ship_order(self) when Shipping::SameDayMethod shipping_method.ship_order(self) end end ... end
44. class Order ... def ship(shipping_method) shipping_method.ship_order(self) end ... end
45. Started to depend on an abstractions, not on concrete implementations RECAP
46. S O L I D Dependency Inversion
47. module Shipping class WikedCrazyMethod < BaseMethod ... def fold(items, origin, destination) ... end def fly ... end ... end end
48. Contract tests
49. shared_examples "a shipping method" do it do should respond_to(:ship_order). with(1).argument end it “can be used to ship an order” do order = Order.new shipping_method = subject expect(order).to_not be_shipped order.ship(shipping_method) expect(order).to be_shipped end end
50. describe Shipping::StandardMethod do subject { Shipping::WikedCrazyMethod } it_should_behave_like "a shipping method” ... end
51. .................................. .................................. ....................... Finished in 129600.024296s 91 examples, 1 failure, 0 skips
52. module Shipping class WikedCrazyMethod < BaseMethod def self.ship_order(order) items = order.items * Math::PI origin = order.seller.name.reverse new.fold(items, origin, order.buyer).fly end ... end end
53. .................................. .................................. ....................... Finished in 129600.024296s 91 examples, 0 failures, 0 skips
54. All clases conform with the same contract RECAP
55. S O L I D Liskov Substitution
56. Subclasses should be substitutable for their base classes
57. Shipping cost calculation Formula that considers: • The amount of items (except for digital items). • A value that represents the distance between the origin and the destination . • A value that represents a fixed rate. items_quantity * distance * fixed_rate
58. • Initial status: a change on any formula items, requires changing the class • Requirement: if only one formula item is changed the rest of the items shouldn’t be affected Shipping cost calculation
59. describe Shipping::Cost do describe "#calculate" do ... subject { Shipping::StandardMethod.new(order, origin, destination) } context "when all items in the order are digital" do ... end context "when exactly one item in the order is not digital" do context "when the origin and destination are in the same state" do ... end context "when the origin and destination are in the same country" do ... end context "when the origin and destination are in different countries" do ... end end context "when more than one item in the order are not digital" do context "when the origin and destination are in the same state" do ... end context "when the origin and destination are in the same country" do ... end context "when the origin and destination are in different countries" do ... end end context "when origin city doesn't ship to the destination" do ... end end ... end
60. module Shipping class Cost def initialize(order, origin, destination) ... end def calculate items_quantity * rate * distance end ... private def items_quantity @order.items.reject(:digital?).lenght end def rate if items_quantity > 1 9.99 else 5.99 end end def distance return 0 if @origin.does_not_ship_to? @destination return 1 if @origin.same_state? @destination return 2 if @origin.same_country? @destination 3 end end end
61. Burroteca
63. Donkey + Discotheque
65. describe Shipping::Cost do ... describe "#calculate" do subject { Shipping::StandardMethod.new(order, origin, destination) } context "when all items in the order are digital" do ... end context "when exactly one item in the order is not digital" do context "when the origin and destination are in the same state" do ... end context "when the origin and destination are in the same country" do ... end context "when the origin and destination are in different countries" do ... end end context "when more than one item in the order are not digital" do context "when the origin and destination are in the same state" do ... end context "when the origin and destination are in the same country" do ... end context "when the origin and destination are in different countries" do ... end end context "when the origin city doesn't ship to the destination" do ... end end ... end
66. describe Shipping::Cost do ... describe "#calculate" do subject { Shipping::StandardMethod.new(order, origin, destination) } context "when all items in the order are digital" do ... end context "when exactly one item in the order is not digital" do context "when the origin and destination are in the same state" do ... end context "when the origin and destination are in the same country" do ... end context "when the origin and destination are in different countries" do ... end end context "when more than one item in the order are not digital" do context "when the origin and destination are in the same state" do ... end context "when the origin and destination are in the same country" do ... end context "when the origin and destination are in different countries" do ... end end context "when the origin city doesn't ship to the destination" do ... end end ... end
67. • "when all items in the order are digital” • "when exactly one item in the order is not digital" • "when more than one item in the order are not digital"
68. describe Shipping::Items do describe "#quantity" do context "when all items in the order are digital" do ... end context "when exactly one item in the order is not digital" do ... end context "when more than one item in the order are not digital" do ... end end end
69. describe Shipping::Cost do ... describe "#calculate" do subject { Shipping::StandardMethod.new(order, origin, destination) } context "when all items in the order are digital" do ... end context "when exactly one item in the order is not digital" do context "when the origin and destination are in the same state" do ... end context "when the origin and destination are in the same country" do ... end context "when the origin and destination are in different countries" do ... end end context "when more than one item in the order are not digital" do context "when the origin and destination are in the same state" do ... end context "when the origin and destination are in the same country" do ... end context "when the origin and destination are in different countries" do ... end end context "when the origin city doesn't ship to the destination" do ... end end ... end
70. • "when the origin and destination are in the same state” • "when the origin and destination are in the same country” • "when the origin and destination are in different countries” • "when the origin city doesn't ship to the destination"
71. describe Shipping::Distance do describe "#calculate" do context "when the origin and destination are in the same state" do ... end context "when the origin and destination are in the same country" do ... end context "when the origin and destination are in different countries" do ... end context "when the origin city doesn't ship to the destination" do ... end end end
72. module Shipping class Cost def initialize(order, origin, destination) ... end def calculate items_quantity * rate * distance end private def items_quantity Shipping::Items.new(@order).quantity end def rate if items_quantity > 1 9.99 else 5.99 end end def distance Shipping::Distance.new(origin, destination).calculate end end end
73. .................................. .................................. ....................... Finished in 129600.024296s 91 examples, 0 failures, 0 skips
74. module Shipping class Cost def initialize(order, origin, destination) ... end def calculate items_quantity * rate * distance end private def items_quantity Shipping::Items.new(@order).quantity end def rate Shipping::Rate.new(items_quantity).calculate end def distance Shipping::Distance.new(origin, destination).calculate end end end
75. A class should have one, and only one, reason to change RECAP
76. S O L I D Single Responsibility
77. Steven Seagull was very happy and so were we
78. S O L I D Interface Segregation
79. Make fine-grained interfaces that are client-specific
80. Why should you care?
81. Respond to changing requirements
82. Manage dependencies
83. “I’m not a great programmer; I’m just a good programmer with great habits” Kent Beck
84. The SOLID principles will help you acquire great object design habits
87. Use your best judgement
89. We all follow some sort of principle
90. Choose yours wisely
91. Obrigado @sebasoga
92. Credits • Me at RubyConf Uruguay: https://secure.flickr.com/photos/94260666@N05/14251620082/ • James: https://www.flickr.com/photos/125635394@N08/14894541332/in/photolist-oGbqdL-9neeBd-9neeD3-o8YsWp-osB7nF-oqTkmd-osef7e-9nfoAb-oDxDMY- o9mymh-ooPmHN-o9mAa9-o9mwaf-o9mBVn-o9mBf4-o9nDYM-o9mEds-o9nEaZ-o9mD9L-oqPJSm-ooPvhG-o9nCTk-o9nKtV-ooPnL9-oqz7uD-ooPvxw-o9mAu6- oqz4o8-o9mCpZ-ooPzR1-oqPGfY-oqD4hS-oqz4TM-osB7Kz-ooPv5s-osBfmB-o9mzY5-osBdax-oqz8ar-o9mJj4-o9mH3f-o9mAoy-oqReWV-o9mwVU-o9mEAJ-oqz2Tz- o9mv9N-o9mBia-o9nESR-oqD2xE • Golden Gate Bridge: https://www.flickr.com/photos/salim/402620871/in/photolist-gxzCVN-3gHR9W-5Wkky-7L2Rdu-7uys1-5R11B1- e7CfhP-6DZhWn-38B3gv-4tN2Xq-kAVAG-dUSUQy-6zLofj-Bzxaa-4jmZiD-Bxufq-bfCFgT-5V84Y-n3nkmB-Bzxus-Bzwuu-bVnpiR-n8Vxzv-axiND-ekFJyQ-h881MJ- bdn9iB-dX8ZeH-ba8H-dZcoQ1-5eikhM-cdFJjh-BzwPa-iW215d-5cTsTq-aPkLxV-6u7c4x-eD5M4-hFTq1W-78nwcX-sXd8e-fCMz9o-813icF-39Wstq-ev17J3-nPu9UG- c6bssC-6EDRSs-dQjTmN-axiXV • Gatto Mimmo: https://www.flickr.com/photos/gattomimmo/2125052913/in/photolist-3eqRoo-bRHqDi-akDPPi-9znES-482wnh-57PniE-7k88aj-2eEDEV-4eMsck- NEZ6A-eAR9nm-6c4a3f-c6p92h-2Y3Xp-78ATbn-9cdK3N-48ERpQ-6bANod-guvqG4-NEZ7f-DV4uM-47Xq5i-95D52m-7GfyjG-3E8qR-2vnfir-6qkkAk-d6XrpW-Ey2hB- NEZ6L-8mNVog-fEgakj-7oGZng-7YpL32-6ScqrQ-qPBk1-4Pvgs-93vS3Y-h1Gipq-47XHfB-PsFae-7YsZMh-8mPMr2-h1G7cr-gux5xc-2xcrmY-owS2Tg-8Jt8ro- ddKAb-332pLa • Shaolin Kungfu 1: https://www.flickr.com/photos/larique/3235902917/in/ photolist-5VWRcB-5KpggW-5KpioE-5VWDwg-5Kk2Qp-5Gf7j-4Jntb-4Jnio-4JoKG-4JoeM-4MZ6M-4JnKm-4JoTZ-4Johi-4JoEA-3xWQA- gsor-7t8exA-5VWPb4-5W24MC-gvWkgi-yKgw6-5W226u-5W1U5w-oUZif-8Mo9FE-8Mk5bg-8Modbf-5Kk3Wa-gwdV3T-fAcBQo-xTuHS-fFtqEg-5W1M8y-5W1KgG- oUZii-oV14w-crzuKN-9Hpikx-9HpdF6-9Hsgeh-9Hsa5Q-9HpiUD-9HsaBC-9HpkEg-9HskyJ-9Hs5jC-9Hpgiv-9HpvH2-9Hpd9k • Shaolin Kungfu 2: https://www.flickr.com/photos/larique/3236693046/in/photolist-5W1U5w-oUZif-8Mo9FE-8Mk5bg-8Modbf-5Kk3Wa-gwdV3T-fAcBQo-xTuHS- fFtqEg-5W1M8y-5W1KgG-oUZii-oV14w- crzuKN-9Hpikx-9HpdF6-9Hsgeh-9Hsa5Q-9HpiUD-9HsaBC-9HpkEg-9HskyJ-9Hs5jC-9Hpgiv-9HpvH2-9Hpd9k-9HsjxW-9Hse2b-9HpucM-9Hs7rj-9Hsigj-9Hpnki-9Hpfn K-9HpbAX-9HppSF-9Hs8xd-9HsiEQ-9HscSS-9Hscgw-9HpuJc-9Hps8M-9Hptd4-9Hprfp-9Hso4o-9HpmM8-9HpoSp-9HppnX-9Hs6X9-9Hs3Lm
93. • Shaolin Kungfu 3: https://www.flickr.com/photos/larique/3235896099/in/photolist-5VWPb4-5W24MC-gvWkgi-yKgw6-5W226u-5W1U5w- oUZif-8Mo9FE-8Mk5bg-8Modbf-5Kk3Wa-gwdV3T-fAcBQo-xTuHS-fFtqEg-5W1M8y-5W1KgG-oUZii-oV14w- crzuKN-9Hpikx-9HpdF6-9Hsgeh-9Hsa5Q-9HpiUD-9HsaBC-9HpkEg-9HskyJ-9Hs5jC-9Hpgiv-9HpvH2-9Hpd9k-9HsjxW-9Hse2b-9HpucM-9Hs7rj-9Hsigj-9Hpnki-9Hpfn K-9HpbAX-9HppSF-9Hs8xd-9HsiEQ-9HscSS-9Hscgw-9HpuJc-9Hps8M-9Hptd4-9Hprfp-9Hso4o • Uncle Bob: https://www.flickr.com/photos/moofbong/4206618799/in/ photolist-7pJ2dk-7pMCyY-7pMWo5-7pHWfe-7pMJ7s-7pMSoJ-7pJ16V-7pHSMt-7pHXpr-7pMNVw-7pHL6Z-7pHHPt-7pMGow-7pHMqv-seGMM-seGNW-7j2wCX- seHCx-seHbn-seHx4-seHmT-seHod-seGDJ-seHFq-seHDM-seGEB-seGL1-seHK6-seGHD-seGYT-seHBi-seGFC-seHHY-seH4e-seHiT-seGJp-seGK7-seHsD-seHkn- seHH7-seHxv-seH5f-seH6s-seGGF-seH3p-seHy8-seH9M-seHzx-b1hoEp-Gj1Wx/ • Kent Beck: https://www.flickr.com/photos/skrb/238102518/in/photolist-Hfu8-n3kzQ-n3kWh-n3kkG-7Jnjvu-6foWR2-6foWRa-djMXPd-cWkWKS-oF4y3- oCY4q-7Tx3yN-3p6hoi-4SrHSK-3Uu3Z3-8QyWVd-3paQF1-3p6hcT-3o4296-3o423c-3p62PD-3p62FM-3p62ze-3p6aQz-3p6h26-3paA55-3payDY-3p5VdK-3p5TaV-3p5S x6-3p5Wnc-3p5YdM-3pavp9-3p5Y4B-3pawg1-3pauEh-3pay1L-3patuL-3p5UiB-3p61zD-3paqDq-3parJE-3p5XKn-3paujq-3pavM9-3p5ZFR-3p5SEk-3pavdN-3p5YMZ-3 pauxq • Superheroes: https://www.flickr.com/photos/charlot17/4648822207 • Beware: https://www.flickr.com/photos/atoach/3922401551/in/photolist-AmPFE-2xwi8T-64GFek-6kWVRg-9vAqpD-jiG1mG-4tj1U-cvyg1f-4eHMx9-65XzLZ- czjMeb-6Y6JC8-5Hja23-6YBkjX-7tRTC3-64VB6C-mmd6zP-9LaWU3-7T61c5-kDDFs3-gmYDTg-ekvzx5-9mrc-7JphLV-6x1xw1-atzvpP-5Nz7gs-5y9TPm-nxj3e1- hHNuw9-bpnnzS-7B43Lf-9BMD7M-bvZDbg-jwss4F-bUhfe1-8ype7F-51LBV-n9rWsV-KugGj-dCPvvp-cECRaC-7GjgEU-jMaCY-h66jGg-jGjbF-9jF4P-diSx2r-nsVjAr- ceUeoG • Burroteca: http://www.jackmag.com.co/articles/burroteca/ Credits