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armakuni.com Mutation Testing Berlin PHP UG Billie Thompson

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About me 2 ● Consulting Engineer for Armakuni ● I help “Return creativity & joy to the world of software engineering” ● Quite tall ● Favourite animal is the capybara

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We’ve worked with 3

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What is it? Break your code Ensure a test fails Improve test 4

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Warm-up

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Do you all know your TDD Cycle Red Green Refactor Red 6

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Todo list ● 7 ● TDD ● Demo: When the test doesn’t fail ● When it’s useful ● Demo: Infection

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TDD 8

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Red 9

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Green 10

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Refactor 11

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Red 12

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Demo: Break It

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What happens if the tests pass? 14

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Bowling 15

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Bowling 16

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10 Pins 17

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10 sets of up to 2 rolls 18

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A score card 1 2 3 4 5 6 7 8 9 10 19

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Rules: Standard Set 1 Set 2 Roll 1 Roll 2 Roll 1 Roll 2 Pins 1 1 1 1 Score 1 2 3 4 20

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Rules: Spare Set 1 Set 2 Roll 1 Roll 2 Roll 1 Roll 2 Pins 5 5 1 1 Score 5 10 12 13 21

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Rules: Strike Set 1 Set 2 Roll 1 Roll 2 Roll 1 Roll 2 Pins 10 1 1 Score 10 12 14 22

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Demo: Break It

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What is it? Break your code Ensure a test fails Improve test 25

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Step by Step Build AST Introduce Bug Do Tests Fail? 26

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Step by Step Build AST Introduce Bug Do Tests Fail? Introduce Bug Do Tests Fail? Introduce Bug Do Tests Fail? 27

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28 Infection has 134 ways to break your code

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Todo list ● 29 ✓ TDD ✓ Demo: When the test doesn’t fail ● When it’s useful ● Demo: Infection

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Stefan has inherited a codebase 30

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What bad habit does Stefan have? 31

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Bugs keep appearing 32

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Stefan gets stricter with reviews 33

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Find untested code 34

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Other Use Cases ● 35 ● Open Source Projects ● New languages ● Improving your heuristic toolkit

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Todo list ● 36 ✓ TDD ✓ Demo: When the test doesn’t fail ✓ When it’s useful ● Demo: Infection

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Demo: Infection

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armakuni.com Billie Thompson Thank you! ● https://github.com/armakuni/bad-bowling-kata ● https://infection.github.io/ @PurpleBooth @ArmakuniHQ