anchor.diff:  
     NewBackend = Backend#backend{ewma = NewEwma,
                                 tracking = NewTracking},
  -  ets:insert(connection_ewma, NewBackend),
  +  true = ets:insert(connection_ewma, NewBackend),
     {noreply, State};
   
   handle_cast({set_pending, {IP, Port}}, State) ->
  
positive.code:          {call, ?MODULE, set_pending, [ip_port()]}] ++
          [{call, ?MODULE, pick_backend, [list(oneof(Vips))]} || VipsPresent]).
  
  -endif.
  
negative.code: -record(test_state, {known_vips = sets:new()}).
  
  stop() ->
    gen_server:call(?MODULE, clear),
    gen_server:stop(?MODULE).
  
  proper_test() ->
    [] = proper:module(?MODULE).
  