RDRC 2014: Safety Nets: Learn to code with confidence

Ruby gives you a great power, such as easy Duck Typing. As the saying goes, "With great power there must also comes great responsibility!" It comes at a price. We cannot afford to blow off everything when shipping. That's why it's important to put in place different strategies to help us to catch errors asap, but also to avoid the cruft long term. Like a safety net, they allow you to go forward with more confidence.

presented at RedDotRubyConference 2014 http://www.reddotrubyconf.com/

Code available at https://github.com/8thcolor/rdrc2014-safetynets
Video available at http://www.confreaks.com/videos/4106-rdrc2014-safety-nets-learn-to-code-with-confidence

Transcript

1. Safety Nets: Learn to code with confidence
2. _toch toch Hi, I'm Christophe
3. Belgium
4. Belgium
5. Co-founder of
7. Once upon a time...
8. My wife's job:
9. My wife's job: curing cancer
11. With Ionizing Radiation
12. Side Effects BUT
13. BUT =
14. BUT Complex
15. BUT Long
16. BUT
18. Ineffective
19. Casualties Ineffective
20. Casualties Ineffective Costly Time consuming
21. Casualties Ineffective Broken Equipment Costly Time consuming
22. Casualties Ineffective Broken Equipment Non Availability Costly Time consuming
23. As an Engineer What CAN she do?
24. Catch Errors & Mitigate Risks
25. How?
26. Is it Working?
27. Test Before & During
28. Is it Correct?
29. Peer-Review & Cross-Check
30. Have the Requirements been met?
31. Peer-Review & Process
32. Sounds Familiar?
33. We're Human
34. We make mistakes
36. We can be helped
37. Radiotherapy, Civil Engineering, Manufacturing, … Software Development
38. Safety Nets
42. Be Informed Then Decide
43. Tests Static Analysis Code Review
44. Tests Static Analysis Code Review
46. describe Invoice do let(:item1) { Item.new(20.0, 3) } let(:item2) { Item.new(15.0, 2) } let(:empty_invoice) { Invoice.new } let(:invoice) do tmp = Invoice.new tmp.add_item(item1) tmp.add_item(item2) tmp end
47. it 'returns a zero total when empty' do assert_equal 0, empty_invoice.total end it 'returns a correct total' do assert_equal 90.0, invoice.total end
48. it 'returns a correct total even after updating a previously added item' do assert_equal 90.0, invoice.total item2.quantity = 3 assert_equal 105, invoice.total end end
49. class Invoice def initialize @items = [] end def add_item(item) @items << item end #...
50. #... def total total = 0 @items.each do |item| total += item.price * item.quantity end total end end
52. class Invoice def initialize @items = [] @total = 0 end def add_item(item) @items << item end #...
53. #... def total @items.each do |item| @total += item.price * item.quantity end @total end end
55. #... def total @total = 0 @items.each do |item| @total += item.price * item.quantity end @total end end
56. Check Functionality & Regression
57. BUT What are we Testing?
58. SimpleCov
59. BUT Has someone Launched the Tests
60. BUT "We’re not shipping your machine!"
61. CI & Close to Prod
62. BUT "Who tests the tests?"
63. Mutant
64. Tests Static Analysis Code Review
66. class Invoice #... def total @total = 0 @items.each do |item| @total += item.price * item.quantity end
67. if @country_code == 'BE' vat = 0.21 * @total elsif ['IT','FR','NL','LU','DE'].include?(@country_code) if valid_vat_number? vat = 0 else vat = 0.21 * @total end else vat = 0 end
68. @total += vat @total end #... end
69. $ flog lib/invoice.rb 27.4: flog total 5.5: flog/method average 17.2: Invoice#total lib/invoice.rb:13
71. class Quote #... def total if @country_code == 'BE' vat = 0.21 * @total elsif ['IT','FR','NL','LU','DE'].include?(@country_code) if valid_vat_number? vat = 0 else vat = 0.21 * @total end
72. else vat = 0 end @total + vat end #... end
73. $ flay lib Total score (lower is better) = 116 1) IDENTICAL code found in :if (mass*2 = 116) lib/invoice.rb:21 lib/quote.rb:10
74. class Invoice #... def total @total = 0 @items.each do |item| @total += item.price * item.quantity end
75. class Invoice #... def total @total = calculate_subtotal
76. def calculate_subtotal total = 0 @items.reduce(0) do |total, item| total += item.price * item.quantity end end
78. $ ruby -w lib/invoice.rb lib/invoice.rb:41: warning: shadowing outer local variable - total lib/invoice.rb:40: warning: assigned but unused variable - total
79. $ rubocop lib/invoice.rb Inspecting 1 file W Offenses: ------8<------ lib/invoice.rb:40:5: W: Useless assignment to variable - total. total = 0 ^^^^^
80. lib/invoice.rb:41:26: W: Shadowing outer local variable - total. @items.reduce(0) do |total, item| ^^^^^ lib/invoice.rb:42:7: W: Useless assignment to variable - total. Use just operator +. total += item.price * item.quantity ^^^^^ 1 file inspected, 10 offenses detected
81. def calculate_subtotal @items.reduce(0) do |total, item| total + item.price * item.quantity end end
82. Check Flaws & Smells
83. BUT You could Forget to run
84. CI + devtool/rake
85. BUT False Positives
86. It is common to take a sort of smug satisfaction in reports of colossal failures of automatic systems, but for every failure of automation, the failures of humans are legion. Exhortations to “write better code” plans for more code reviews, pair programming, and so on just don’t cut it, especially in an environment with dozens of programmers under a lot of time pressure. The value in catching even the small subset of errors that are tractable to static analysis every single time is huge. John Carmack
87. Tests Static Analysis Code Review
89. module Vat def self.rate(country_code = '', vat_number = '') if country_code == 'BE' return 0.21 elsif %w(IT FR NL LU DE).include?(country_code) if is_valid?(vat_number) return 0 else return 0.21 end
90. else return 0 end end #... end
91. class Invoice # ... def total @total = calculate_subtotal vat = Vat::rate(@country_code, @vat_number) * @total @total += vat end # ... end
92. class Quote # ... def total vat = Vat::rate(@country_code, @vat_number) * @total @total + vat end # ... end
93. $ flay lib/ Total score (lower is better) = 0
94. class Country # ... def belgium? @code == 'BE' end def europe? %w(IT FR NL LU DE).include? @code end end
95. module Vat def self.rate(country, vat_number = '') if country.belgium? return 0.21 elsif country.europe? if is_valid?(vat_number) return 0 else return 0.21 end # ... end
96. 34.7: flog total 2.9: flog/method average 7.0: Invoice#calculate_subtotal lib/invoice.rb:28 6.7: Invoice#initialize lib/invoice.rb:5 5.7: Invoice#total lib/invoice.rb:16 4.8: Vat::rate lib/vat.rb:2
97. 4.8: Vat::rate lib/vat.rb:2 3.3: branch 1.2: is_valid? 1.1: europe? 1.0: belgium? 1.0: assignment
98. Spreading Knowledge
99. Check Anything
100. BUT Cannot Check Everything Everytime
101. Test + Static Analysis
102. What now?
103. Cost & Risk
104. Don't wait
106. We're only Human
111. ? https://github.com/ 8thcolor/rdrc2014-safetynets _toch toch