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

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Safety Nets How to check your code?

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_toch toch Hi, I'm Christophe

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Belgium

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Belgium

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Founder of

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Once upon a time...

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40% of fatalities = no air

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Peer Review BWRAF

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15% of fatalities = equipment

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Make them Test

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1st cause = Human error

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Be Equipped Be Assisted

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We're Human

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We make mistakes

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We can be helped

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Scuba Diving, Civil Engineering, Manufacturing, … Software Development

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Safety Nets How to check your code?

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Be Informed Then Decide

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Tests Code Review Static Analysis

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Tests Static Analysis Code Review

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Tests Static Analysis Code Review

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Tests Static Analysis Code Review

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❏ tires on? ❏ painted? ❏ tank full? ❏ labelled? ❏ checked on bench?

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Tests Static Analysis Code Review

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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

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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

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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

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class Invoice def initialize @items = [] end def add_item(item) @items << item end #...

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#... def total total = 0 @items.each do |item| total += item.price * item.quantity end total end end

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class Invoice def initialize @items = [] @total = 0 end def add_item(item) @items << item end #...

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#... def total @items.each do |item| @total += item.price * item.quantity end @total end end

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#... def total @total = 0 @items.each do |item| @total += item.price * item.quantity end @total end end

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Check Functionality & Regression

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BUT What are we Testing?

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SimpleCov

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BUT Has someone Launched the Tests

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BUT "We’re not shipping your machine!"

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CI & Close to Prod

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BUT "Who tests the tests?"

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Mutant

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Tests Static Analysis Code Review

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class Invoice #... def total @total = 0 @items.each do |item| @total += item.price * item.quantity end

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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

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@total += vat @total end #... end

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$ flog lib/invoice.rb 27.4: flog total 5.5: flog/method average 17.2: Invoice#total lib/invoice.rb:13

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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

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else vat = 0 end @total + vat end #... end

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$ 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

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class Invoice #... def total @total = 0 @items.each do |item| @total += item.price * item.quantity end

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class Invoice #... def total @total = calculate_subtotal

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def calculate_subtotal total = 0 @items.reduce(0) do |total, item| total += item.price * item.quantity end end

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$ 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

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$ rubocop lib/invoice.rb Inspecting 1 file W Offenses: ------8<------ lib/invoice.rb:40:5: W: Useless assignment to variable - total. total = 0 ^^^^^

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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

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def calculate_subtotal @items.reduce(0) do |total, item| total + item.price * item.quantity end end

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Check Flaws & Smells

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BUT You could Forget to run

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CI + devtool/rake

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BUT False Positives

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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

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Tests Static Analysis Code Review

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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

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else return 0 end end #... end

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class Invoice # ... def total @total = calculate_subtotal vat = Vat::rate(@country_code, @vat_number) * @total @total += vat end # ... end

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class Quote # ... def total vat = Vat::rate(@country_code, @vat_number) * @total @total + vat end # ... end

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$ flay lib/ Total score (lower is better) = 0

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class Country # ... def belgium? @code == 'BE' end def europe? %w(IT FR NL LU DE).include? @code end end

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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

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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

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4.8: Vat::rate lib/vat.rb:2 3.3: branch 1.2: is_valid? 1.1: europe? 1.0: belgium? 1.0: assignment