apache_beam.io.gcp.pubsub_integration_test.PubSubIntegrationTest.test_streaming_data_only is flaky

self = <apache_beam.io.gcp.pubsub_integration_test.PubSubIntegrationTest testMethod=test_streaming_data_only>

    @pytest.mark.it_postcommit
    def test_streaming_data_only(self):
>     self._test_streaming(with_attributes=False)

apache_beam/io/gcp/pubsub_integration_test.py:209: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
apache_beam/io/gcp/pubsub_integration_test.py:205: in _test_streaming
    timestamp_attribute=self.TIMESTAMP_ATTRIBUTE)
apache_beam/io/gcp/pubsub_it_pipeline.py:93: in run_pipeline
    result = p.run()
apache_beam/pipeline.py:573: in run
    return self.runner.run_pipeline(self, self._options)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

self = <apache_beam.runners.dataflow.test_dataflow_runner.TestDataflowRunner object at 0x7face48c99e8>
pipeline = <apache_beam.pipeline.Pipeline object at 0x7face48c9278>
options = <apache_beam.options.pipeline_options.PipelineOptions object at 0x7face4891588>

    def run_pipeline(self, pipeline, options):
      """Execute test pipeline and verify test matcher"""
      test_options = options.view_as(TestOptions)
      on_success_matcher = test_options.on_success_matcher
      wait_duration = test_options.wait_until_finish_duration
      is_streaming = options.view_as(StandardOptions).streaming
    
      # [BEAM-1889] Do not send this to remote workers also, there is no need to
      # send this option to remote executors.
      test_options.on_success_matcher = None
    
      self.result = super().run_pipeline(pipeline, options)
      if self.result.has_job:
        # TODO(markflyhigh)(BEAM-1890): Use print since Nose dosen't show logs
        # in some cases.
        print('Worker logs: %s' % self.build_console_url(options))
    
      try:
        self.wait_until_in_state(PipelineState.RUNNING)
    
        if is_streaming and not wait_duration:
          _LOGGER.warning('Waiting indefinitely for streaming job.')
        self.result.wait_until_finish(duration=wait_duration)
    
        if on_success_matcher:
          from hamcrest import assert_that as hc_assert_that
>         hc_assert_that(self.result, pickler.loads(on_success_matcher))
E         AssertionError: 
E         Expected: (Test pipeline expected terminated in state: RUNNING and Expected 4 messages.)
E              but: Expected 4 messages. Got 0 messages. Diffs (item, count):
E           Expected but not in actual: dict_items([(b'data001-seen', 1), (b'data002-seen', 1), (b'data003\xab\xac-seen', 1), (b'data004\xab\xac-seen', 1)])
E           Unexpected: dict_items([])

apache_beam/runners/dataflow/test_dataflow_runner.py:68: AssertionError