code: def test_serial_time_single(self):
      v = self.client.load_balanced_view()
      ar = v.apply_async(time.sleep, 0.25)
      with pytest.raises(TimeoutError):
          ar.serial_time
      ar.get(2)
      assert ar.serial_time < 1.0
      assert ar.serial_time > 0.2
  
imports: import os
  import time
  from datetime import datetime
  import pytest
  from IPython.utils.io import capture_output
  import ipyparallel
  from ipyparallel import error
  from .clienttest import ClusterTestCase, raises_remote
label_desc: Use image node_id 18 for calling the TestAsyncResult obj's underlying member method code with example usage: obj.test_serial_time_single() without return types