anchor.diff:      {stop, normal, ok, S}.
   
   %% @hidden
  +handle_cast({add_history, _Item}, #state{history=undefined}=S) ->
  +    {noreply, S};
   handle_cast({add_history, Item}, S) ->
       {noreply, S#state{history = [Item| S#state.history]}};
   handle_cast(_Msg, S)  ->
  
positive.code: -record(state, {mod :: atom(),
                  expects :: dict(),
                  valid = true :: boolean(),
                  history = [] :: history(),
                  original :: term(),
                  was_sticky :: boolean()}).
  
  
negative.code: handle_call({delete, Func, Arity}, _From, S) ->
      NewExpects = delete_expect(S#state.mod, {Func, Arity}, S#state.expects),
      {reply, ok, S#state{expects = NewExpects}};
  handle_call(history, _From, #state{history=undefined}=S) ->
      {reply, [], S};
  handle_call(history, _From, S) ->
      {reply, lists:reverse(S#state.history), S};
  handle_call(reset, _From, S) ->
  