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Mutation testing 101 Form3 Friday Sharing 25th June 2019

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

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“Internal” vs “External” quality The system / component / whatever behaves as expected... ● https://martinfowler.com/articles/microservice-testing/ ● Specification by example / ATDD / BDD ● Example mapping ● Functional testing ● Contract testing ● Exploration testing ● Performance testing ● Penetration testing ● etc...

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Metrics, metrics everywhere... ● Cyclomatic complexity ● Duplications ● Code smells ● Maintainability ● Technical debt ● Test duration ● Test coverage: are we covering all the “possible” behaviours of the system? https://sonarcloud.io/dashboard?id=com.islomar.payments%3Apayments-api

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“Tell me how you measure me, and I will tell you how I will behave” Eliyahu M. Goldratt “You get what you measure”

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assertTrue(true);

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

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

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

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

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Return values mutator

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

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Demo time

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Demo time (in Java… 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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Final considerations ● High test coverage means almost NOTHING. Low test coverage is a smell... ● Mutation testing: only for isolated tests (aka “unit tests”): 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 “incremental analysis” (experimental feature)

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

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