Debug Test Failures in Merge Requests with Duo

Concise guide to using Duo to diagnose and suggest fixes for test failures in a merge request.

🪄 Using Duo to Debug and Fix Test Failures in Your Merge Request

When your merge request has a failing test, use Duo to quickly determine if it’s related to your changes and get a suggested fix.

💡 Tip: Consider retrying the job immediately in case it’s a transient failure. If it fails again, proceed with the debugging steps below.

  1. Navigate to your MR pipeline and locate the failing job

  2. Open the failing job that displays the test failure

  3. Invoke GitLab Duo in the job log view (press d or click the Duo button in the top right corner)

    📝 Note: Duo will automatically truncate lengthy job logs by removing the middle section. For greater accuracy, you can copy and paste the specific stack trace and error message into your prompt.

    🌐 For browser-based tests: Duo cannot download artifacts automatically. If needed, you can manually download the DOM from the /tmp/capybara directory (feature specs) or failure_screenshots directory (E2E tests) in the job artifacts and paste it into your prompt to help Duo debug browser-based failures. This also applies to other artifacts such as application logs.

  4. Clear previous context to avoid confusion with other MRs:

       /clear

  5. Prompt: Check if the test failure is widespread:

       I have a test failure in this job. Can you:
   1. Check recent issues at https://gitlab.com/gitlab-org/quality/engineering-productivity/master-broken-incidents/-/issues and https://gitlab.com/gitlab-org/quality/engineering-productivity/approved-mr-pipeline-incidents/-/issues/ to see if this failure is occurring in other merge requests or in master
   2. Let me know if this appears to be related to my MR changes or a widespread issue

  6. Prompt: If the failure appears to be related to the changes in the MR, prompt for a fix:

       Can you analyze what's causing this failure and provide a fix? Please:
   1. Infer the test type from the test file path
   2. Explain what's causing the failure
   3. If this is a stale test (test needs updating), provide a diff to fix the test
   4. If this is a bug in the application, explain the bug and provide a diff to fix the application code

✅ What to expect:

  • Duo will provide a diff for specific code changes required
  • Always review suggestions carefully before applying them
  • Test the fix locally if possible before committing

⚠️ When Duo Can’t Help

If Duo’s analysis does not resolve your issue, follow these steps in order:

  1. 🔍 Verify it’s a known failure (< 2 minutes):
    • Check the Danger bot comment on your MR under the “Pipelines failing on master” section for links to known master-broken issues
    • Scan #master-broken (master branch failures) and #mr-blocked-by-master-broken (approved MR failures) Slack channels
  2. 💻 Try reproducing locally (~10 minutes):
    • Execute the test against your GDK to confirm if it’s environment-specific or a genuine issue
  3. 🚧 Request quarantine if needed:

📚 Related Resources

Need help? Reach out in #s_developer_experience or create a Request for Help issue

Last modified December 1, 2025: Add page for debugging MR test failures with Duo guide (167845ea)
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