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Refactoring legacy code using Approval testing (Meetup Alicante)

Refactoring legacy code using Approval testing (Meetup Alicante)

Slides used during the Software Crafters Meetup session.
The session had two parts:
* An introduction and open discussion about concepts like legacy code and technical debt.
* A live-coding session to show a technique called "approval testing", applying it to cover with tests some "legacy code".

https://www.meetup.com/es-ES/Software-Crafters-Alicante/events/267849996/

Isidro López

January 22, 2020
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  1. Refactoring legacy code using
    approval testing
    Meetup SW Crafters Alicante, 22.01.2020
    @islomar

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  2. Ego slide
    Hemos venido a jugar...
    Desarrollador de software/producto
    @islomar
    [email protected]

    Teleco, Antropología Social y
    Cultural, Executive MBA, CSM…

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  3. What is legacy code for you?

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  4. 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

    Code that you would prefer not to touch

    ?

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  5. What is technical debt for you?

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  6. Is technical debt always "bad"?

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  7. Debt metaphor by Ward Cunningham (1992)
    “Shipping first time code is like going into debt. A little debt
    speeds development so long as it is paid back promptly with a
    rewrite.
    [...] The danger occurs when the debt is not repaid.”

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  8. About technical debt

    The extra effort that it takes to keep on working on the code
    is the interest paid on the debt.

    It slows you down in baby steps, not realizing and taking for
    granted that “it is the way it is”.

    OK in isolated and stable areas which are “never” touched.

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

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  10. How to refactor (complex) legacy code?

    We do not have tests as safety net before starting to refactor!

    But… what if it is not really clear what is the current behavior?

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  11. 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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  13. Live Coding time!!
    https://github.com/islomar/approval-testing

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  14. Resources: kata and approval testing
    ● Kata
    ○ Description of the kata
    ○ https://github.com/emilybache/GildedRose-Refactoring-Kata
    ○ https://github.com/emilybache/GildedRose-Approval-Kata
    ○ http://coding-is-like-cooking.info/2013/03/writing-good-tests-for-the-gilded
    -rose-kata/
    ● Approval testing
    ○ https://www.infoq.com/news/2017/02/approval-testing-texttest
    ○ http://approvaltests.com/

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  15. Resources: screencasts and books
    ● Screencasts
    ○ Refactoring legacy code with approval testing (Emily Bache)
    ○ Approval tests with Lift Kata (Emily Bache)
    ○ Testing and refactoring legacy code (Sandro Mancuso)
    ○ Approval tests with Java
    ● Emily Bache
    ○ https://www.praqma.com/stories/all/#emilybache
    ○ https://github.com/emilybache
    ○ How to develop new features with approval testing

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  16. Resources: refactoring and technical debt

    Original writing about technical debt from Ward Cunningham

    The Debt Metaphor (video)

    Tech Debt - MPJ's Musings - Fun Fun Function
    ● https://martinfowler.com/bliki/TechnicalDebt.html
    ● https://martinfowler.com/bliki/TechnicalDebtQuadrant.html
    ● https://www.fluentcpp.com/2020/01/17/technical-debt-is-like-a-tetris-game/
    ● https://martinfowler.com/bliki/DesignPayoffLine.html
    ● https://martinfowler.com/bliki/DesignStaminaHypothesis.html
    ● https://martinfowler.com/articles/workflowsOfRefactoring/
    ● https://www.praqma.com/stories/advanced-testing-refactoring-techniques/

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