Using code coverage and mutation testing to add tests to legacy code

Refactoring is a key skill needed when working with legacy code bases, and the easiest / safest way to do it is with good test coverage. But what if your legacy code base has no tests? This talk shows, with examples, how to use code coverage and mutation testing to add tests to your legacy code base.

This talk was delivered at MenderCon online on Thurs 16th May 2024: https://mendercon.com/schedule/#session-9

Transcript

1. @ClareSudbery MenderCon ‘24 Use code coverage and mutation testing to add tests to legacy code
2. Useful links from today Useful Links @ClareSudbery
3. Untested legacy code Add tests before refactoring @ClareSudbery When would you do this?
4. …because safe, confident refactoring rocks! @ClareSudbery When would you do this?
5. Landing in a neat pair-synchronized way. https://www.instagram.com/p/BsY1qBeg5Qg @ClareSudbery
6. Bamboo, by No Fit State
7. @ClareSudbery https://www.geepawhill.org/2021/09/29/many-more-much-smaller-steps-first-sketch/
8. Demo: Using code coverage to add tests to existing code @ClareSudbery Using coverage to add tests
9. Code coverage tools @ClareSudbery Using coverage to add tests
10. @ClareSudbery Use coverage to find missing test data Doing the exercise yourself • Original code is here: https://github.com/emilybache/GildedRose-Refactoring-Kata • Requirements are in the readme • Run this command to clone the code: • git clone https://github.com/emilybache/GildedRose-Refactoring-Kata.git • Choose your language • My demo code is here: https://github.com/claresudbery/GildedRose-Refactoring- Kata/blob/coverage-demo-complete/csharpcore/GildedRoseTests/GildedRoseTest.cs
11. Demo Using mutation testing to improve your test suite @ClareSudbery Using mutation testing to improve tests
12. @ClareSudbery • Original code is here: https://github.com/emilybache/GildedRose-Refactoring-Kata • Requirements are in the readme • Run this command to clone the code: • git clone https://github.com/emilybache/GildedRose-Refactoring-Kata.git • Choose your language • My demo code is here: https://github.com/claresudbery/GildedRose-Refactoring- Kata/blob/csharp-mutation-complete/csharpcore/GildedRoseTests/GildedRoseTest.cs Use mutation testing to find missing untested edge cases Doing the exercise yourself
13. Questions? @ClareSudbery Using coverage and mutation testing to add and improve tests
14. Useful links from today Useful Links @ClareSudbery
15. I hosted a podcast… https://www.madetech.com/podcast/ @ClareSudbery
16. Relevant podcast episodes… @ClareSudbery Test Driven Development: tinyurl.com/mtb-geepaw-hill Refactoring: tinyurl.com/mtb-emily-bache Balancing Change: tinyurl.com/kevlin-henney-twitter Changing legacy systems: tinyurl.com/meri-williams- twitter
18. Sudbery Software Engineering Ltd Does your team want help to improve their software delivery? Coaching, keynotes & workshops Events and info: tinyurl.com/csudbery Mastodon: mastodon.social/@ClareSudbery LinkedIn: tinyurl.com/lin-csudbery Podcast: tinyurl.com/tech-better-pod
19. Thank you!