Safety Nets: How to check your code? (in Ruby)

Programming gives you a great power...

But as the saying goes, "With great power comes great responsibility!"

As software developers, 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 cruft in the long term. Come and discover those tools & techniques (Tests, Code Review, Static Analysis) and how to put them in place in your code base. Like safety nets, they will allow you to go forward with more confidence.

http://www.meetup.com/Le-Wagon-Brussels-Coding-Station/events/222354764/

Transcript

1. Safety Nets How to check your code?
2. _toch toch Hi, I'm Christophe
3. Belgium
4. Belgium
5. Founder of
7. Once upon a time...
9. 40% of fatalities = no air
10. Peer Review BWRAF
11. 15% of fatalities = equipment
12. Make them Test
13. 1st cause = Human error
14. Be Equipped Be Assisted
15. We're Human
16. We make mistakes
18. We can be helped
19. Scuba Diving, Civil Engineering, Manufacturing, … Software Development
20. Safety Nets How to check your code?
24. Be Informed Then Decide
25. Tests Code Review Static Analysis
26. Tests Static Analysis Code Review
30. Tests Static Analysis Code Review
32. Tests Static Analysis Code Review
33. ❏ tires on? ❏ painted? ❏ tank full? ❏ labelled? ❏ checked on bench?
34. Tests Static Analysis Code Review
36. 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
37. 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
38. 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
39. class Invoice def initialize @items = [] end def add_item(item) @items << item end #...
40. #... def total total = 0 @items.each do |item| total += item.price * item.quantity end total end end
42. class Invoice def initialize @items = [] @total = 0 end def add_item(item) @items << item end #...
43. #... def total @items.each do |item| @total += item.price * item.quantity end @total end end
45. #... def total @total = 0 @items.each do |item| @total += item.price * item.quantity end @total end end
46. Check Functionality & Regression
47. BUT What are we Testing?
48. SimpleCov
49. BUT Has someone Launched the Tests
50. BUT "We’re not shipping your machine!"
51. CI & Close to Prod
52. BUT "Who tests the tests?"
53. Mutant
54. Tests Static Analysis Code Review
56. class Invoice #... def total @total = 0 @items.each do |item| @total += item.price * item.quantity end
57. 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
58. @total += vat @total end #... end
59. $ flog lib/invoice.rb 27.4: flog total 5.5: flog/method average 17.2: Invoice#total lib/invoice.rb:13
61. 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
62. else vat = 0 end @total + vat end #... end
63. $ 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
64. class Invoice #... def total @total = 0 @items.each do |item| @total += item.price * item.quantity end
65. class Invoice #... def total @total = calculate_subtotal
66. def calculate_subtotal total = 0 @items.reduce(0) do |total, item| total += item.price * item.quantity end end
68. $ 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
69. $ rubocop lib/invoice.rb Inspecting 1 file W Offenses: ------8<------ lib/invoice.rb:40:5: W: Useless assignment to variable - total. total = 0 ^^^^^
70. 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
71. def calculate_subtotal @items.reduce(0) do |total, item| total + item.price * item.quantity end end
72. Check Flaws & Smells
73. BUT You could Forget to run
74. CI + devtool/rake
75. BUT False Positives
76. 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
77. Tests Static Analysis Code Review
79. 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
80. else return 0 end end #... end
81. class Invoice # ... def total @total = calculate_subtotal vat = Vat::rate(@country_code, @vat_number) * @total @total += vat end # ... end
82. class Quote # ... def total vat = Vat::rate(@country_code, @vat_number) * @total @total + vat end # ... end
83. $ flay lib/ Total score (lower is better) = 0
84. class Country # ... def belgium? @code == 'BE' end def europe? %w(IT FR NL LU DE).include? @code end end
85. 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
86. 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
87. 4.8: Vat::rate lib/vat.rb:2 3.3: branch 1.2: is_valid? 1.1: europe? 1.0: belgium? 1.0: assignment
88. Spreading Knowledge
89. Check Anything
90. BUT Cannot Check Everything Everytime
91. Test + Static Analysis
92. What now?
93. Cost & Risk
94. Don't wait
96. We're only Human
101. ? https://github.com/ 8thcolor/rdrc2014-safetynets _toch toch