# File test/test_logger.rb, line 296
    def test_err
      spin_lock = true
      NUM_OF_THREAD.times do
        @th_grp.add Thread.new{
          while (spin_lock)
            # ready to start.
          end
          NUM_OF_CALL.times do
            @logger.err("HALO\n")
          end
        }
      end
      spin_lock = false
      for thread in @th_grp.list
        thread.join
      end
      assert_equal(NUM_OF_THREAD * NUM_OF_CALL, @err_call)
    end