   #
   # **Usage:**
   #
-  #     queue.blocked_groups (groups) -> YOUR OWN CODE
+  #     queue.blocked_groups (err, groups) -> YOUR CODE
   #
   blocked_groups: (callback) ->
     @redis.smembers @key('BLOCKED'), (err, res) ->

  #
  # **Usage:**
  #
  #     queue.slowest_tasks (tasks) -> YOUR CODE HERE
  #
  # `slowest_tasks` is an asynchronous method. The only arg of the callback
  # function is an array of slowest tasks in the reverse order by processing

  #     - poll task from the `SOURCE` queue.
  #   + **failed**, then inspect the passed in argument, retry or block
  #   according to the `do` property of the error object.
  #
  # Calling the callback function is the responsibility of you. Otherwise
  # `Fairy` will stop dispatching tasks.
