Important
We're excited you're checking out Hegel! Hegel is in beta, and we'd love for you to try it and report any feedback.
As part of our beta, we may make breaking changes if it makes Hegel a better property-based testing library. If that instability bothers you, please check back in a few months for a stable release!
See https://hegel.dev/compatibility for more details.
hegel-rust is a property-based testing library for Rust. hegel-rust is based on Hypothesis, using the Hegel protocol.
To install: cargo add --dev hegeltest.
Hegel will use uv to install the required hegel-core server component.
If uv is already on your path, it will use that, otherwise it will download a private copy of it to ~/.cache/hegel and not put it on your path.
See https://hegel.dev/reference/installation for details.
Here's a quick example of how to write a Hegel test:
use hegel::generators as gs;
use hegel::TestCase;
fn my_sort(ls: &[i32]) -> Vec<i32> {
let mut result: Vec<i32> = ls.to_vec();
result.sort();
result.dedup();
result
}
#[hegel::test]
fn test_matches_builtin(tc: TestCase) {
let mut vec1 = tc.draw(gs::vecs(gs::integers::<i32>()));
let vec2 = my_sort(&vec1);
vec1.sort();
assert_eq!(vec1, vec2);
}This test will fail when run with cargo test! Hegel will produce a minimal failing test case for us:
Draw 1: [0, 0]
thread 'test_matches_builtin' (2) panicked at src/main.rs:15:5:
assertion `left == right` failed
left: [0, 0]
right: [0]
Hegel reports the minimal example showing that our sort is incorrectly dropping duplicates. If we remove result.dedup() from my_sort(), this test will then pass (because it's just comparing the standard sort against itself).