Getting a Handle on Legacy Code

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www .codingzeal.com @codingzeal Randy Coulman Getting a Handle on Legacy Code Senior Software Engineer @randycoulman

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Welcome to our new job! Enhance the inventory management system for the Gilded Rose Inn

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The System

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The System • Items have a sell_in value: the number of days we have to sell the item

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The System • Items have a sell_in value: the number of days we have to sell the item • Items have a quality value: how valuable the item is

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The System • Items have a sell_in value: the number of days we have to sell the item • Items have a quality value: how valuable the item is • At the end of each day our system lowers both values for every item

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The Spec: Can We Trust It? • Once the sell-by date has passed, quality degrades twice as fast • The quality of an item is never negative • “Aged Brie" actually increases in quality the older it gets • The quality of an item is never more than 50 • "Sulfuras", being a legendary item, never has to be sold or decreases in quality • "Backstage passes", like aged brie, increases in quality as its sell-by date approaches; quality increases by 2 when there are 10 days or less and by 3 when there are 5 days or less, but quality drops to 0 after the concert.

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Constraint The Item class and @items property are off-limits No collective code ownership

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Our Task: Support Conjured items Conjured items degrade in quality twice as fast as normal items

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Workshop Structure Mix of: • Presentation/demo • Mob programming • Small group/pair/individual work

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Mob Programming • One computer for programming • One driver • N navigators and researchers http://mobprogramming.org/mob-programming-basics/

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Legacy Code How do we safely change legacy code?

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The Legacy Code Algorithm

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The Legacy Code Algorithm 1. Identify change points

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The Legacy Code Algorithm 1. Identify change points 2. Find test points

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The Legacy Code Algorithm 1. Identify change points 2. Find test points 3. Break dependencies

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The Legacy Code Algorithm 1. Identify change points 2. Find test points 3. Break dependencies 4. Write tests

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The Legacy Code Algorithm 1. Identify change points 2. Find test points 3. Break dependencies 4. Write tests 5. Make changes and refactor

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The Legacy Code Algorithm https://twitter.com/mfeathers/status/589118880825495552

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Code For the Workshop https://github.com/CodingZeal/gilded-rose-railsconf2015

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The Code

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Mob Programming Exercise Write characterization tests

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Golden Master Testing a.k.a. Guru Checks Output anti-pattern Katrina Owen’s Approvals Gem

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Mob Programming Exercise Use Approvals to simplify testing

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Cleaning Up the Code Fight the urge to rewrite

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Cleaning Up the Code The Boy Scout Rule: "Leave the campground cleaner than you found it"

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Cleaning Up the Code Baby Steps Lots of tiny, safe refactorings add up to big changes

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Cleaning Up the Code Don’t Boil the Ocean Stay focused

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Cleaning Up the Code https://twitter.com/KentBeck/status/250733358307500032

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Cleaning Up the Code https://twitter.com/supermoof/status/478322429257715712

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Mob Programming Exercise Refactor for better test points

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Small Group Exercise Write a few more-targeted tests

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Small Group Exercise Refactor enough to add new feature

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Mob Programming Exercise More refactoring

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Public Service Announcement

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Want More? Original Gilded Rose Kata http://craftsmanship.sv.cmu.edu/katas/gilded-rose-kata Gilding the Rose Talk at GoGaRuCo 2014 http://confreaks.tv/videos/gogaruco2014-gilding-the-rose-refactoring-legacy-code Code from GoGaRuCo 2014 Talk https://github.com/randycoulman/GildedRose

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References Working Effectively With Legacy Code: Michael Feathers http://www.amazon.com/Working-Effectively-Legacy-Michael-Feathers/dp/0131177052 Refactoring: Martin Fowler http://www.amazon.com/Refactoring-Improving-Design-Existing-Code/dp/0201485672

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References Approvals https://github.com/kytrinyx/approvals SimpleCov https://github.com/colszowka/simplecov Flog https://github.com/seattlerb/ﬂog

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Questions ? http://randycoulman.com http://speakerdeck.com/randycoulman http://speakerrate.com/randycoulman Code is on Github https://github.com/CodingZeal/gilded-rose-railsconf2015

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www .codingzeal.com @codingzeal Thank You! Randy Coulman @randycoulman