anchor.diff:  
   add_piece_update_case({N, Time, Pid}) ->
       {ok, Ref, _} = ?scarcity:watch(9, nine, pieces([0,2,4,6])),
  -    ok = ?scarcity:add_peer(9, pieces([])),
  -    ok = ?scarcity:add_piece(9, 2, pieces([2])),
  +    ok = ?scarcity:add_peer(N, pieces([])),
  +    ok = ?scarcity:add_piece(N, 2, pieces([2])),
       ?assertEqual(5000, ?timer:step(Time)),
       ?assertEqual(1, ?timer:fire(Time)),
       receive
  
positive.code:     ?assertEqual(Pid, ?scarcity:lookup_scarcity_server(1)).
  
  initial_ordering_case({N, Time, Pid}) ->
      {ok, Order} = ?scarcity:get_order(2, pieces([0,1,2,3,4,5,6,7])),
      ?assertEqual([0,1,2,3,4,5,6,7], Order).
  
  empty_ordering_case({N, Time, Pid}) ->
  
negative.code: peer_exit_update_case({N, Time, _}) ->
      Main = self(),
      Pid = spawn_link(fun() ->
          ok = ?scarcity:add_peer(N, pieces([0,1,2,3])),
          Main ! done,
          receive die -> ok end
      end),
      receive done -> ok end,
      {ok, Ref, _} = ?scarcity:watch(N, ten, pieces([0,2,4,6])),
      Pid ! die,
      ?assertEqual(1, ?timer:fire(Time)),
      receive
  