let%expect_test _ =
  let print_list print_ele xs =
    let rec iter pre post = function
      | [] -> print_string post
      | x :: xs ->
        print_string pre;
        print_ele x;
        iter ";" "]" xs
    in
    iter "[" "[]" xs
  in
  let print_ints_nl xs = print_list print_int xs; print_newline () in

  let wh = Wheel.make 4 in
  (* t=0 *)
  Wheel.add wh 1 |> ignore;
  Wheel.add wh 2 |> ignore;
  Wheel.add wh 3 |> ignore;
  (* t=1 *)
  print_ints_nl (Wheel.tick wh); [%expect {| [] |}];
  Wheel.add wh 4 |> ignore;
  Wheel.add wh 5 |> ignore;
  (* t=2 *)
  print_ints_nl (Wheel.tick wh); [%expect {| [] |}];
  Wheel.add wh 6 |> ignore;
  (* t=3 *)
  print_ints_nl (Wheel.tick wh); [%expect {| [] |}];

  let every = ref [] in
  Wheel.iter (fun x -> every := x :: !every) wh;
  print_ints_nl (List.sort compare !every); [%expect {| [1;2;3;4;5;6] |}];

  (* t=0 *)
  print_ints_nl (Wheel.tick wh); [%expect {| [1;2;3] |}];
  (* t=1 *)
  print_ints_nl (Wheel.tick wh); [%expect {| [4;5] |}];
  (* t=2 *)
  print_ints_nl (Wheel.tick wh); [%expect {| [6] |}];
  (* t=3 *)
  print_ints_nl (Wheel.tick wh); [%expect {| [] |}];
  (* t=0 *)
  print_ints_nl (Wheel.tick wh); [%expect {| [] |}];