# File lib/test/unit/util/observable.rb, line 51
        def remove_listener(channel_name, listener_key)
          channel = channels[channel_name]
          return nil unless (channel)
          key = listener_key
          if (listener_key.instance_of?(Proc))
            key = ProcWrapper.new(listener_key)
          end
          if (channel.has_key?(key))
            return channel.delete(key)
          end
          return nil
        end