garage/fuzz/src/lib.rs

use garage_table::crdt::Crdt;
use std::fmt::Debug;

pub fn check_crdt_laws<T>(a: T, b: T, c: T)
where
	T: Crdt + PartialEq + Clone + Debug,
{
	// Idempotency: merge(a, a) == a
	{
		let mut a2 = a.clone();
		a2.merge(&a);
		assert_eq!(a2, a, "merge is not idempotent: {a2:#?} != {a:#?}");
	}

	// Commutativity: merge(a, b) == merge(b, a)
	let ab = {
		let mut t = a.clone();
		t.merge(&b);
		t
	};
	let ba = {
		let mut t = b.clone();
		t.merge(&a);
		t
	};
	assert_eq!(ab, ba, "merge is not commutative: {ab:#?} != {ba:#?}");

	// LX's corrolary: merge(merge(a,b),b) = merge(a,b)
	let ab_b = {
		let mut t = ab.clone();
		t.merge(&b);
		t
	};
	assert_eq!(ab, ab_b);

	// Associativity: merge(merge(a, b), c) == merge(a, merge(b, c))
	let ab_c = {
		let mut t = ab;
		t.merge(&c);
		t
	};
	let bc = {
		let mut t = b;
		t.merge(&c);
		t
	};
	let a_bc = {
		let mut t = a;
		t.merge(&bc);
		t
	};
	assert_eq!(
		ab_c, a_bc,
		"merge is not associative: {ab_c:#?} != {a_bc:#?}"
	);
}