chore(pubsub): Topic race condition; SMT test failure

[briandorsey]

Description

TestCreateSubscriptionWithSMT has been failing in repo-wide builds with a nil topic error.

• update getOrCreateTopic test function to avoid race between checking topic existence and creating the topic. (tests are using t.Parallel(), so it can happen across tests)
• in TestCreateSubscriptionWithSMT:
  • use shared getOrCreateTopic rather than local code. (local code had a bug which only occured when topic didn't already exist.)
  • use test specific topicID
  • use only one Retry block in body of the test so new topic both lives long enough to run the test and is cleaned up by defer.

Helps fix tests failing in Renovate PR #5225

Checklist

• I have followed Contributing Guidelines from CONTRIBUTING.MD
• Tests pass: go test -v ./.. (see Testing)
• Code formatted: gofmt (see Formatting)
• Vetting pass: go vet (see Formatting)
• Please merge this PR for me once it is approved

[gemini-code-assist]

Summary of Changes

Hello @briandorsey, 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 a persistent test failure in TestCreateSubscriptionWithSMT by resolving a race condition in topic creation and refactoring the test's setup. The changes enhance the reliability and isolation of the test, ensuring consistent behavior across parallel executions and proper resource management.

Highlights

• Race Condition Fix: The getOrCreateTopic helper function was updated to prevent a race condition that could occur when parallel tests checked for topic existence and then attempted to create it. The new logic attempts to create the topic first and handles AlreadyExists errors.
• Test Refactor: The TestCreateSubscriptionWithSMT function was refactored to utilize the shared and improved getOrCreateTopic helper, replacing its previous local topic creation logic which had a bug.
• Test Isolation: A test-specific topic ID is now used within TestCreateSubscriptionWithSMT to ensure better isolation and prevent conflicts with other tests.
• Test Reliability: The TestCreateSubscriptionWithSMT now uses a single Retry block, ensuring the topic lives long enough for the test to complete and is properly cleaned up via defer.

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[gemini-code-assist]

Code Review

This pull request effectively resolves a race condition in the getOrCreateTopic test helper by adopting an 'act-then-check' strategy. It also rectifies a failing test, TestCreateSubscriptionWithSMT, by utilizing this improved helper, employing a test-specific topic ID, and ensuring proper resource cleanup. The changes are well-reasoned and correctly address the reported issues. My review includes a suggestion to enhance error message formatting for improved debuggability in the test helper.