Tests for security; Test for design

Many people come to the world of test driven development because of the security it provides. However, when done correctly TDD provides loads of other benefits; specifically it can help us design better software.

In this talk we'll discuss tools and techniques to drive better designs with tests. Specifically we'll talk about test isolation with mocks and stubs, test speed, designing apis, and more. Everyone will leave with a better understanding of how to utilize TDD and BDD to create not just safer code, but better code.

Transcript

1. Tests for Design Tests for Security Chris Keathley / @ChrisKeathley / keathley.io
2. Who is doing TDD?
3. Who likes doing TDD?
4. Change
5. Change is hard
6. Change is inevitable
7. Change is good
8. Change is our responsibility
9. Design
10. Design is hard
11. Design must be flexible
12. Design for purpose
13. Tests
14. I love tests
15. Zen
16. Tests provide guard rails.
17. Focus
18. Empower Refactoring
19. “Refactoring without tests is just moving crap around”
20. “Refactoring without tests is just moving crap around” - me (just now)
21. Protection from Regression
22. Protip: Managers love the idea of security
23. There are bugs in your code.
24. All of this is good
25. But is isn’t everything
26. Test Driven Design
27. Lets talk about…
28. Lets talk about… TDD 101
29. Lets talk about… TDD 101 Commands and Queries
30. Lets talk about… TDD 101 Commands and Queries Designing Apis
31. Lets talk about… TDD 101 Commands and Queries Designing Apis Test Speed
32. A note for those who are feeling pedantic
33. “Any sufficiently complicated test suite contains an ad hoc, informally- specified, bug-ridden, slow implementation of half of Erlang” - also me (also just now)
34. TDD 101
35. Methodology
36. Methodology Write a failing test
37. Methodology Write a failing test Make that test pass
38. Methodology Write a failing test Make that test pass Refactor
39. Methodology Write a failing test Make that test pass Refactor
40. describe Platypus do it "can drink" do end end
41. describe Platypus do it "can drink" do expect(platypus.stomach).to include coffee end end
42. describe Platypus do it "can drink" do platypus.drink(coffee) expect(platypus.stomach).to include coffee end end
43. describe Platypus do it "can drink" do platypus = Platypus.new coffee = Coffee.new(grams: 400) platypus.drink(coffee) expect(platypus.stomach).to include coffee end end
44. We know too much implementation
45. describe Platypus do it "can drink" do platypus = Platypus.new coffee = Coffee.new(grams: 400) platypus.drink(coffee) expect(platypus.stomach).to include coffee end end Exposes Data
46. describe Platypus do it "can drink" do platypus = Platypus.new coffee = Coffee.new(grams: 400) platypus.drink(coffee) expect(platypus.drank?(coffee)).to eql(true) end end
47. class Platypus def initialize @stomach = [] end def drink(coffee) @stomach << coffee end def drank?(coffee) @stomach.include?(coffee) end end
48. Rely on interfaces and hide state
49. But is this the right interface?
50. describe Platypus do describe "when it drinks coffee" do it "becomes energized" do end end end
51. describe Platypus do describe "when it drinks coffee" do it "becomes energized" do expect(platypus.energized?).to eql(true) end end end
52. describe Platypus do describe "when it drinks coffee" do it "becomes energized" do expect(platypus.energized?).to eql(true) end end end
53. describe Platypus do describe "when it drinks coffee" do it "becomes energized" do platypus = Platypus.new expect(platypus.energized?).to eql(true) end end end
54. describe Platypus do describe "when it drinks coffee" do it "becomes energized" do platypus = Platypus.new platypus.drink(Coffee.new(grams: 400)) expect(platypus.energized?).to eql(true) end end end
55. class Platypus def initialize @stomach = [] end def drink(coffee) @stomach << coffee end def energized? @stomach.any? end end
56. Think about your interfaces
57. Test your boundaries
58. Commands & Queries
59. OO is about messages
60. Object
61. Object Queries
62. Object Queries Commands
63. Queries Commands Return things Change things
64. describe Platypus do describe "when it drinks coffee" do it "becomes energized" do platypus = Platypus.new platypus.drink(Coffee.new(grams: 400)) expect(platypus.energized?).to eql(true) end end end
65. describe Platypus do describe "when it drinks coffee" do it "becomes energized" do platypus = Platypus.new platypus.drink(Coffee.new(grams: 400)) expect(platypus.energized?).to eql(true) end end end Query
66. describe Platypus do describe "when it drinks coffee" do it "becomes energized" do platypus = Platypus.new platypus.drink(Coffee.new(grams: 400)) expect(platypus.energized?).to eql(true) end end end Command Query
67. Designing Apis - Queries
68. describe Platypus do describe "when it drinks coffee" do it "gains energy" do end end end
69. describe Platypus do describe "when it drinks coffee" do it "gains energy" do expect(platypus.energy).to eql(45) end end end
70. describe Platypus do describe "when it drinks coffee" do it "gains energy" do platypus = Platypus.new expect(platypus.energy).to eql(45) end end end
71. describe Platypus do describe "when it drinks coffee" do it "gains energy" do platypus = Platypus.new platypus.drink(coffee) expect(platypus.energy).to eql(45) end end end
72. describe Platypus do describe "when it drinks coffee" do it "gains energy" do platypus = Platypus.new coffee = double(energy: 50) platypus.drink(coffee) expect(platypus.energy).to eql(45) end end end
73. describe Platypus do describe "when it drinks coffee" do it "gains energy" do platypus = Platypus.new coffee = double(energy: 50) platypus.drink(coffee) expect(platypus.energy).to eql(45) end end end Assert the result
74. class Platypus def initialize @stomach = [] end def drink(coffee) @stomach << coffee end def energy @stomach .map { |item| item.energy } .reduce { |acc, i| acc + i } end end
75. class Platypus def initialize @stomach = [] end def drink(coffee) @stomach << coffee end def energy @stomach.map(&:energy).reduce(:+) * 0.90 end end
76. Design collaborating interfaces
77. Interfaces MUST be enforced
78. describe Coffee do describe "#energy" do it "calculates the energy per gram" do coffee = Coffee.new(grams: 400) expect(coffee.energy).to eql(115) end end end
79. class Coffee def initialize(grams:) @grams = grams end def energy ((@grams / 17.42) * 5).round end end
80. Keep interfaces flexible
81. class Bacon def initialize(grams:) @grams = grams end def energy 9001 end end
82. Queries Assert only the reponse.
83. Queries Don’t expect external calls
84. Queries Provide doubles if the interface is unknown or takes too long to build.
85. Designing Apis - Commands
86. describe Platypus do describe "when it waddles" do it "wears out its shoes" do end end end
87. describe Platypus do describe "when it waddles" do it "wears out its shoes" do expect(shoes).to receive(:wear) end end end
88. describe Platypus do describe "when it waddles" do it "wears out its shoes" do shoes = Shoes.new expect(shoes).to receive(:wear) end end end
89. describe Platypus do describe "when it waddles" do it "wears out its shoes" do shoes = Shoes.new expect(shoes).to receive(:wear) platypus.waddle! end end end
90. describe Platypus do describe "when it waddles" do it "wears out its shoes" do shoes = Shoes.new platypus = Platypus.new(shoes: shoes) expect(shoes).to receive(:wear) platypus.waddle! end end end
91. describe Platypus do describe "when it waddles" do it "wears out its shoes" do shoes = Shoes.new platypus = Platypus.new(shoes: shoes) expect(shoes).to receive(:wear) platypus.waddle! end end end Outgoing Command
92. class Platypus def initialize(shoes:) @shoes = shoes @stomach = [] end def waddle! @shoes.wear end end
93. class Platypus def initialize(shoes:) @shoes = shoes @stomach = [] end def waddle! @shoes.wear end end Dependency Injection
94. describe Platypus do describe "when it waddles" do it "wears out its shoes" do shoes = Shoes.new platypus = Platypus.new(shoes: shoes) expect(shoes).to receive(:wear) platypus.waddle! expect(platypus.shod?).to eql(false) end end end
95. class Platypus def initialize(shoes:) @shoes = shoes @stomach = [] end def waddle! @shoes.wear end def shod? @shoes.good_condition? end end
96. class Shoes def initialize @worn = false end def wear @word = true end def good_condition? !@worn end end
97. Expect outgoing commands to be sent
98. Commands Assert all side effects
99. Commands Inject dependencies
100. Commands Mock outgoing calls
101. Test Speed
102. Fast tests are important
103. TDD requires feedback
104. Isolate from other dependencies
105. Test at the lowest possible level
106. Write fewer tests!
107. Conclusion
108. Test Interfaces
109. Test once
110. Test everything
111. Test for design
112. Security will follow
113. Prepare for change
114. Thanks! Chris Keathley / @ChrisKeathley / keathley.io