How do you find a lot of non-obvious bugs in an afternoon? Write a property that should always be true (like "this code should have the same result before and after it's optimized"), generate random valid expressions, and study the counter-examples!

Property-based testing is a powerful technique for finding bugs quickly. It can partly replace unit tests, leading to a more flexible test suite that generates more cases and finds more bugs in less time.

It's really quick and easy to get started with property-based testing. You can use existing tools like QuickCheck, or write your own: Andy Windo and I wrote pflua-quickcheck and found a half-dozen bugs with it in one afternoon, using pure Lua and no external libraries.

In this talk, I will introduce property-based testing, demonstrate a tool for using it in Lua - and how to write your own property-based testing tool from scratch, and explain how simple properties found bugs in pflua.