anchor.diff:      NewNodes = [{Node, joinning}|State#state.nodes],
       % TODO: health checks, if 'Node' is healthy, node status changes 
       %       alive.
  -    {noreply, NewNodes};
  +    {noreply, State#state{nodes = NewNodes}};
   handle_cast(_Msg, State) ->
       {noreply, State}.
   
  
positive.code: %%% @doc
  %%% Adds some user's task based on schedule
  %%%
  %%% @spec add_task(binary()) -> term()
  %%% @end
  -spec add_task(binary(), schedule(), detail()) -> term().
  add_task(Task, Schedule, Detail) -> gen_server:call(?SERVER, {add, Task, Schedule, Detail}).
  
  %%% @doc
  %%% Cancels the task
  %%%
  %%% @spec cancel_task(binary()) -> term().
  %%% @end
  -spec cancel_task(binary()) -> term().
  cancel_task(Task) -> gen_server:call(?SERVER, {cancel, Task}).
  
  %%% @doc
  %%% Shows the registered schedule of the task.
  %%%
  %%% @spec show_schedule(binary()) -> term().
  %%% @end
  -spec show_schedule(binary()) -> term().
  show_schedule(Task) -> gen_server:call(?SERVER, {show, Task}).
  
negative.code: %%                                   {stop, Reason, State}
  %% @end
  %%--------------------------------------------------------------------
  handle_call({add, TaskName, Schedule, Detail}, _From, State) ->
      Task = {TaskName, Schedule, Detail},
      %% TODO: receive a message from task worker
      NewTasks = [Task|State#state.tasks],
      io:format("adds a task: ~p", [Task]),
      {reply, ok, State#state{ tasks = NewTasks }};
  handle_call({cancel, _Task}, _From, State) ->
      Reply = ok,
      {reply, Reply, State};
  