#[test]
#[should_panic]
fn ub_find() {
    #[derive(Resource, Default)]
    struct SyncCounter(RwLock<()>);

    fn assert_non_sync(counter: Res<SyncCounter>) {
        // Panic if multiple instances of this system try to access `counter` at once.
        let _guard = counter.0.try_write().unwrap();

        // Make sure other systems have a chance to conflict with this one before dropping the guard.
        std::thread::sleep(std::time::Duration::from_millis(100));
    }

    let mut world = World::default();
    world.init_resource::<SyncCounter>();

    let mut stage = SystemStage::parallel()
        .with_system(assert_non_sync)
        .with_system(assert_non_sync)
        .with_system(assert_non_sync);

    stage.run(&mut world);
}