anchor.diff:  
   get_ewma_or_default({IP, Port}) ->
     case ets:lookup(connection_ewma, {IP, Port}) of
  -    [{_Addr, ExistingBackend}] ->
  +    [ExistingBackend] ->
         ExistingBackend;
  -    _ ->
  +    [] ->
         #backend{ip_port = {IP, Port}}
     end.
   
  
positive.code: -record(test_state, {known_vips = sets:new()}).
  
  stop() ->
    gen_server:call(?MODULE, clear).
  
  proper_test() ->
    [] = proper:module(?MODULE).
  
negative.code:          {call, ?MODULE, set_pending, [ip_port()]}] ++
          [{call, ?MODULE, pick_backend, [list(oneof(Vips))]} || VipsPresent]).
  
  state_test() ->
    TestTuple = {{1, 2, 3, 4}, 5000},
    {ok, State} = init([]),
    ?assertEqual([], ets:lookup(connection_ewma, TestTuple)),
    {noreply, State} = handle_cast({set_pending, TestTuple}, State),
    ?assertNotEqual([], ets:lookup(connection_ewma, TestTuple)),
    Backend = get_ewma_or_default(TestTuple),
    EWMA = Backend#backend.ewma,
    ?assertEqual(1, EWMA#ewma.pending),
    ets:delete(connection_ewma).
  -endif.
  