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About code reviews
and BUGS
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Famous software in history
● 1962 - NASA Mariner 1 mission, spacecraft destroyed
○ 18 million USD
● 1988 - Morris Worm experiment at MIT
○ 50.000 USD
● 1994 - Pentium FDIV
○ 475 million USD
● 2010 - Mt. Gox bitcoin exchange
○ 850.000 bitcoins
● 2012 - Knight Capital Group investments
○ 440 million USD
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The cost of a
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Test failure while
coding, immediate fix
1 €
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A colleague spots a bug
during code review,
few minutes fix
10 €
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During QA testing, receive a
vague bug report, spend time
reproducing it, write the fix
and release after an hour
100 €
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In production, different users
spot the a bug “it just don’t
work”, 8 hours of work
1000 €
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Too many defects, release
postponed by few weeks
10.000 €
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Too many defects and missing
features, release postponed by
months 100.000 €
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Release to production even
with many defects and
missing features: bad user
experience, loss of credibility
project failure
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Good to have practices to the rescue
● Source code VC
● Bug tracker
● Dependency Management
● Configuration Management
● Automated deployment
● Continuous Integration
● Data management
● Continuous delivery
● Code reviews
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CODE
REVIEWS
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1. Write code
2. Ask for feedback
3. Repeat until OK
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WHY
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Find bugs before
your customers do
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Meets specifications
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Shared ownership
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Keep the bar high
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Leave a written trail
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Mentorship by default
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Asynchronous feedback
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HOW
(as a submitter)
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Avoid wall of diff
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Contain not
interesting changes
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Solve one thing at a
time
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Provide context
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Highlight most
interesting points
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Respect for your
colleagues time
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HOW
(as a reviewer)
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Be polite
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Learn context
before starting
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Give feedback that helps
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Look for missing tests
and edge cases
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Pay attention to
what tools can’t find
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our process
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