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Hegel is a property-based testing library for Go. Hegel is based on Hypothesis, using the Hegel protocol.

To install: go get hegel.dev/go/hegel@latest.

Hegel for Go drives libhegel — the native Rust engine. At runtime hegel-go looks for libhegel.so (Linux), libhegel.dylib (macOS), or libhegel.dll (Windows) at $HEGEL_LIBHEGEL_PATH first, then in a sibling ../hegel-rust/target/release/ (and ../hegel-rust/target/debug/) checkout relative to your project root, and finally falls back to downloading the matching version from hegel-rust's GitHub releases on first use (cached under ~/.cache/hegel-go/libhegel/<version>/, SHA-256 verified). Set HEGEL_LIBHEGEL_NO_DOWNLOAD=1 to opt out of the download fallback.

Supported platforms (those with a published libhegel artifact): Linux amd64/arm64, macOS arm64 (Apple Silicon), and Windows amd64/arm64.

During development, build the library locally:

just build-libhegel    # cargo build --release -p hegeltest-c in ../hegel-rust/

Here's a quick example of how to write a Hegel test:

package example_test

import (
	"math"
	"slices"
	"testing"

	"hegel.dev/go/hegel"
)

func mySort(ls []int) []int {
	result := make([]int, len(ls))
	copy(result, ls)
	slices.Sort(result)
	result = slices.Compact(result)
	return result
}

func TestMatchesBuiltin(t *testing.T) {
	hegel.Test(t, func(ht *hegel.T) {
		slice1 := hegel.Draw(ht, hegel.Lists(hegel.Integers(math.MinInt, math.MaxInt)))
		slice2 := mySort(slice1)
		slices.Sort(slice1)
		if !slices.Equal(slice1, slice2) {
			ht.Fatalf("slices not equal: %v != %v", slice1, slice2)
		}
	})
}

This test will fail when run with go test! Hegel will produce a minimal failing test case for us:

example_test.go:46: slice1 := hegel.Draw(ht, hegel.Lists(hegel.Integers(math.MinInt, math.MaxInt))) = []int{0, 0}
example_test.go:50: slices not equal: [0 0] != [0]

Hegel reports the minimal example showing that our sort is incorrectly dropping duplicates. If we remove result = slices.Compact(result) from mySort(), this test will then pass (because it's just comparing the standard sort against itself).