“Imperative” property testing and the `arbtest` crate

2025-05-01

Came across a new crate for property testing in Rust. It's called `arbtest`, written by matklad.

It aims to provide a simpler API than `quickcheck` and `proptest`. In particular, it follows the pattern of “imperative property testing”. Instead of using macro wizardry to inject random instances of a fixed set of datatypes, you are provided a source of random data, and it's up to you to generate whatever data you need by drawing bits from that random data source. In this aspect, it's similar to `rapid` on the Go side.

I came across this via an interesting path: Tony Finch described an “element-wise” approach to testing a data structure (as opposed to the more common “example-wise”), which was in response to a matklad post about “swarm testing” data structures. matklad mentioned `arbtest` in passing in a comment on the Lobsters discussion for the original post.