anchor.diff:      ].
   
   
  -append_metrics_test_() ->
  -    [?_assertEqual(#{"foo" => [1]}, append_metrics("foo", 1, #{})),
  -     ?_assertEqual(#{"foo" => [2, 1]}, append_metrics("foo", 2, #{"foo" => [1]})),
  -     ?_assertEqual(#{"foo" => [8, 1], "bar" => 34}, append_metrics("foo", 8, #{"foo" => [1], "bar" => 34})),
  -     ?_assertEqual(#{"foo" => 9}, append_metrics("foo", 9, #{"foo" => 9}))
  +record_metrics_test_() ->
  +    [?_assertEqual(#{"foo" => [1]}, record_metrics("foo", 1, #{})),
  +     ?_assertEqual(#{"foo" => [2, 1]}, record_metrics("foo", 2, #{"foo" => [1]})),
  +     ?_assertEqual(#{"foo" => [8, 1], "bar" => 34}, record_metrics("foo", 8, #{"foo" => [1], "bar" => 34})),
  +     ?_assertEqual(#{"foo" => 9}, record_metrics("foo", 9, #{"foo" => 9}))
       ].
   
   
  
positive.code: -export([start_link/0,
           increment/1,
           increment/2,
           append/2]).
  
  %% gen_server callbacks
  -export([init/1,
  
negative.code:     Map = increment_metrics(Key, Amount, State#state.metrics),
      {noreply, State#state{metrics=Map}};
  
  handle_cast({record, Key, Value}, State) ->
      Map = record_metrics(Key, Value, State#state.metrics),
      {noreply, State#state{metrics=Map}};
  
  handle_cast(_Msg, State) ->
  