Fix flaky PubSub integration test by deduplicating messages

[shunping]

PubSub guarantees at-least-once delivery, which can result in duplicate messages being pulled during the test. Deduplicate the received messages by message ID to prevent assertion failures on message count, while still acknowledging all received delivery attempts.

Failed test example:
https://github.com/apache/beam/actions/runs/28270530203/job/83766777493?pr=39130

Traceback:

___________ PubSubIntegrationTest.test_batch_write_with_ordering_key ___________
[gw1] linux -- Python 3.12.13 /runner/_work/beam/beam/build/gradleenv/417525525/bin/python3

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

    @pytest.mark.it_postcommit
    def test_batch_write_with_ordering_key(self):
      """Test WriteToPubSub in batch mode with ordering keys.
    
      Dataflow's Native Pub/Sub Sink does not support ordering_key
      (see https://github.com/apache/beam/issues/36201), so this test
      only applies to runners using Beam's Python WriteToPubSub Sink.
      Dataflow users should use the XLang WriteToPubSub path instead
      (apache_beam.io.external.gcp.pubsub.WriteToPubSub with
      publish_with_ordering_key=True).
      """
      if self.runner_name == 'TestDataflowRunner':
        self.skipTest(
            'Dataflow Native PubSub Sink does not support ordering_key '
            '(see https://github.com/apache/beam/issues/36201).')
      from google.pubsub_v1.types import Subscription
    
      from apache_beam.options.pipeline_options import PipelineOptions
      from apache_beam.options.pipeline_options import StandardOptions
      from apache_beam.transforms import Create
    
      ordering_topic = self.pub_client.create_topic(
          name=self.pub_client.topic_path(
              self.project, 'psit_topic_ordering' + self.uuid))
      ordering_sub = self.sub_client.create_subscription(
          request=Subscription(
              name=self.sub_client.subscription_path(
                  self.project, 'psit_sub_ordering' + self.uuid),
              topic=ordering_topic.name,
              enable_message_ordering=True,
          ))
      time.sleep(10)
    
      try:
        test_messages = [
            PubsubMessage(
                b'order_data001', {'attr': 'value1'}, ordering_key='key1'),
            PubsubMessage(
                b'order_data002', {'attr': 'value2'}, ordering_key='key1'),
            PubsubMessage(
                b'order_data003', {'attr': 'value3'}, ordering_key='key2'),
        ]
    
        pipeline_options = PipelineOptions()
        pipeline_options.view_as(StandardOptions).streaming = False
    
        with TestPipeline(options=pipeline_options) as p:
          messages = p | 'CreateMessages' >> Create(test_messages)
          _ = messages | 'WriteToPubSub' >> WriteToPubSub(
              ordering_topic.name,
              with_attributes=True,
              publish_with_ordering_key=True)
    
        time.sleep(10)
    
        # Retry pulling to handle PubSub delivery delays
        received_messages = []
        deadline = time.time() + 60  # wait up to 60 seconds
        while time.time() < deadline:
          response = self.sub_client.pull(
              request={
                  'subscription': ordering_sub.name,
                  'max_messages': 10,
              })
          received_messages.extend(response.received_messages)
          if len(received_messages) >= len(test_messages):
            break
          time.sleep(5)
    
>       self.assertEqual(len(received_messages), len(test_messages))
E       AssertionError: 4 != 3

apache_beam/io/gcp/pubsub_integration_test.py:377: AssertionError

[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses flakiness in the PubSub integration tests caused by duplicate message deliveries. By introducing a deduplication mechanism based on message IDs, the test now correctly validates the expected number of unique messages received, ensuring stable execution in environments where Pub/Sub may deliver messages more than once.

Highlights

• Message Deduplication: Implemented message deduplication using message IDs to account for Pub/Sub's at-least-once delivery guarantee, preventing test failures due to duplicate message counts.
• Robust Acknowledgement: Updated the acknowledgement logic to collect all received message IDs and conditionally perform the acknowledgement only if messages were retrieved.

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[gemini-code-assist]

Code Review

This pull request updates the Pub/Sub integration test to deduplicate received messages by message_id and handle potential duplicate deliveries. The reviewer suggests acknowledging messages immediately inside the pull loop to prevent redeliveries caused by the 10-second acknowledgment deadline, which also allows for the removal of the redundant post-loop acknowledgment block.

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[github-actions]

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R: @tvalentyn for label python.

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