Refactoring legacy code using Approval testing

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Refactoring legacy code using approval testing CSAT Lunch & Learn, 01.02.2019 @islomar

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What is legacy code for you?

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For some people, legacy code is about... ● Code not developed by me ● Code that you don't know ● Code without tests ● Code difficult to maintain (difficult to understand or change) ● Code no longer supported ● ?

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What is technical debt for you?

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Is technical debt always "bad"?

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Technical Debt Quadrant https://martinfowler.com/bliki/TechnicalDebtQuadrant.html

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How to refactor (complex) legacy code? ● But… what if it is not really clear what is the current behavior? ● We do not have tests as safety net before starting to refactor!

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Approval testing to the rescue!! It also exists something called Golden Master "Approval testing is a test technique which compares the current output of your code with an "approved" version. The approved version is created by initially examining the test output and approving the result." Assume the current behaviour is correct: the first goal is to refactor in a safe way!!

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Gilded Rose refactoring kata Description of the kata https://github.com/emilybache/GildedRose-Refactoring-Kata https://github.com/emilybache/GildedRose-Approval-Kata https://github.com/islomar/approval-testing http://approvaltests.com/

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Interesting resources ● https://www.praqma.com/stories/advanced-testing-refactoring-techniques/ ● https://www.infoq.com/news/2017/02/approval-testing-texttest ● http://coding-is-like-cooking.info/2013/03/writing-good-tests-for-the-gilded-ros e-kata/ ● https://martinfowler.com/bliki/TechnicalDebt.html ● https://martinfowler.com/bliki/TechnicalDebtQuadrant.html

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Interesting resources ● Screencasts ○ Screencast: refactoring legacy code with approval testing (Emily Bache) ○ Screencast: testing and refactoring legacy code (Sandro Mancuso) ○ Approval tests with Java ● Books ○ https://www.goodreads.com/book/show/44936.Refactoring ○ Working effectively with legacy code (Michael Feathers)