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Safety Nets:
Learn to code
with confidence
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_toch toch
Hi, I'm
Christophe
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Belgium
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Belgium
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Co-founder of
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Once upon a
time...
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My
wife's job:
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My
wife's job:
curing
cancer
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With
Ionizing
Radiation
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Side Effects
BUT
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BUT
=
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BUT
Complex
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BUT
Long
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BUT
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Ineffective
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Casualties Ineffective
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Casualties Ineffective
Costly Time
consuming
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Casualties Ineffective
Broken
Equipment
Costly Time
consuming
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Casualties Ineffective
Broken
Equipment
Non
Availability
Costly Time
consuming
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As an Engineer
What CAN she do?
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Catch Errors
&
Mitigate Risks
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How?
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Is it Working?
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Test Before & During
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Is it Correct?
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Peer-Review & Cross-Check
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Have the
Requirements
been met?
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Peer-Review & Process
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Sounds
Familiar?
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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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Radiotherapy,
Civil Engineering,
Manufacturing,
…
Software Development
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Safety
Nets
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Be Informed
Then Decide
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Tests
Static Analysis
Code Review
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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
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Spreading
Knowledge
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Check
Anything
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BUT
Cannot Check
Everything
Everytime
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Test
+
Static Analysis
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What now?
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Cost & Risk
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Don't wait
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We're only
Human
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No content
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?
https://github.com/
8thcolor/rdrc2014-safetynets
_toch toch