Property-testing all* the things in SerenityOS

*: not all the things.

I’m a big proponent of property-based testing (as in, QuickCheck or Hypothesis), be it in Elm, Haskell, Scala or JavaScript - it’s great at finding tricky edge cases, refining your understanding of your system and giving you confidence it works for more cases than just your happy path unit tests.

Imagine my horror when I saw that SerenityOS, my favorite “watch and admire it from distance” open source project didn’t have any support for property-based testing! There were three options: don’t test at all, test with unit tests, or fuzz the binary as a black box.

I set out to write a property-based testing framework for SerenityOS, complete with automatic shrinking and all, and to use it to write property tests for apps and libraries all across SerenityOS.

In this talk I want to share that journey, the surprising complications and how I overcame them, the tests I’ve written and categories they fall into, and the bugs I’ve found.

Martin Janiczek

Fediverse: @janiczek@functional.cafe
Twitter: @janiczek

Martin Janiczek is an Elm developer based in Czech Republic writing complex UIs at Vendr. Into piano and bass, making pizza, programming language design, property based tests, algebraic data types and functional programming in general.