in timer/src/lib.rs [260:269]
fn add() {
let mut wheel = Wheel::new(1000);
let _id = wheel.add(0, 0);
assert_eq!(wheel.pending(), 1);
assert_eq!(wheel.next_timeout(), Some(0));
let timers = wheel.tick(1);
assert_eq!(timers.len(), 1);
assert_eq!(wheel.pending(), 0);
assert_eq!(wheel.next_timeout(), None);
}