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Mutation testing 101

Mutation testing聽101

OK, so... you write tests to verify that your code is doing what it is expected to do. But who verifies that the tests are "good"? We all know that test coverage means "almost" nothing, so... Who watches the watchmen?

This will be an introduction talk and demo to mutation testing 馃檪

Isidro L贸pez

June 21, 2019
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  1. Mutation testing 101
    Form3 Friday Sharing
    25th June 2019

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  3. https://i.ytimg.com/vi/QUyPALAJFpU/maxresdefault.jpg

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  4. 鈥淚nternal鈥 vs 鈥淓xternal鈥 quality
    The system / component / whatever behaves as expected...

    https://martinfowler.com/articles/microservice-testing/

    Speci铿乧ation by example / ATDD / BDD

    Example mapping

    Functional testing

    Contract testing

    Exploration testing

    Performance testing

    Penetration testing

    etc...

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  6. Metrics, metrics everywhere...

    Cyclomatic complexity

    Duplications

    Code smells

    Maintainability

    Technical debt

    Test duration

    Test coverage: are we covering all the 鈥減ossible鈥 behaviours of the system?
    https://sonarcloud.io/dashboard?id=com.islomar.payments%3Apayments-api

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  7. 鈥淭ell me how you measure me,
    and I will tell you how I will behave鈥
    Eliyahu M. Goldratt
    鈥淵ou get what you measure鈥

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  8. assertTrue(true);

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  10. https://www.wallpaperup.com/865120/X-MEN_superhero_marvel_action_adventure_sci-fi_warrior_fantasy_fighting_hero_xmen_1xmena_com
    ics_poster.html
    Mutation testing to the rescue!!

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  11. https://www.guru99.com/mutation-testing.html

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  12. Simple examples of mutators

    Conditional boundaries

    Increments

    Invert negatives

    Math

    Negation

    Return values

    Void method calls

    Constructor calls

    Empty returns

    False/True returns

    Remove conditionals

    etc...

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  13. Conditional boundaries mutators
    http://pitest.org/quickstart/mutators/

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  14. Negate conditional mutators
    http://pitest.org/quickstart/mutators/

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  15. Math mutators
    http://pitest.org/quickstart/mutators/

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  16. Return values mutator

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  17. Void method call mutator
    http://pitest.org/quickstart/mutators/

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  18. Demo time

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  19. Demo time (in Java鈥 oopsss!!)
    https://github.com/islomar/payments-api
    https://github.com/islomar/parrotter
    https://github.com/sandromancuso/Gilded-Rose-Kata (100% test coverage)

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  20. Final considerations

    High test coverage means almost NOTHING. Low test coverage is a smell...

    Mutation testing: only for isolated tests (aka 鈥渦nit tests鈥): tests which are fast
    (FIRST)

    Start with the basic mutators

    Depending on the complexity and size of the code, it can be very time/resource
    consuming, watch out!! (combinatorial explosion)

    In Pitest you can activate 鈥渋ncremental analysis鈥 (experimental feature)

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  21. Resources (I)
    GOTO 2015: Mutation testing in Python
    https://www.youtube.com/watch?v=jwB3Nn4hR1o
    Mutation testing in Python with Cosmic Ray
    https://vimeo.com/171319754
    Vicen莽 Garc铆a en SCBCN (in Spanish)
    https://www.youtube.com/watch?v=LWL71b2fc64
    Madrid JUG (in Spanish)
    https://www.youtube.com/watch?v=hk_urzWGqrE

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  22. Resources (II)
    https://www.slideshare.net/RafaelVindelAmor/who-watches-the-watchmen-mutation-te
    sting-75767706
    https://www.st.cs.uni-saarland.de/edu/testingdebugging10/slides/10-MutationTesting.pdf
    https://hackernoon.com/mutmut-a-python-mutation-testing-system-9b9639356c78

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  23. https://looneytunes.fandom.com/wiki/That%27s_all_Folks

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