Remove flaky assertion in FullClusterRestartIT.testRecovery

[andrross]

The test asserts that after a full cluster restart upgrade, at least one old version Lucene segment must still exist on the primary. This is not guaranteed because background merges can merge all old version segments into new segments before the assertion runs.

The remaining assertions still validate that translog replay occurred and produced at least one new-version segment on the primary.

Related Issues

Resolves #15813

Check List

• Functionality includes testing.

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[github-actions]

PR Code Analyzer ❗

AI-powered 'Code-Diff-Analyzer' found issues on commit 83fc653.

Path	Line	Severity	Description
qa/full-cluster-restart/src/test/java/org/opensearch/upgrades/FullClusterRestartIT.java	796	low	Removal of a backward-compatibility assertion (`assertNotEquals` for `numBwcVersion`) in a full-cluster-restart upgrade test. This weakens test coverage by no longer verifying that at least one old-version segment exists after translog recovery. While this could be a legitimate fix for a flaky test or a change in expected upgrade behavior, silently dropping upgrade-validation assertions in a security-sensitive context (data integrity during cluster restart) is worth reviewing to confirm intent.

The table above displays the top 10 most important findings.

Total: 1 | Critical: 0 | High: 0 | Medium: 0 | Low: 1

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[github-actions]

PR Reviewer Guide 🔍

Here are some key observations to aid the review process:

🧪 No relevant tests

🔒 No security concerns identified

✅ No TODO sections

🔀 No multiple PR themes

⚡ Recommended focus areas for review Reduced Coverage Removing the assertion that validates at least one old-version (BWC) segment exists reduces test coverage for verifying that the upgrade scenario actually preserved old segments before merging. While the PR description explains this is flaky due to background merges, consider whether an alternative approach (e.g., disabling merges during the test or checking segment counts before merges occur) could preserve this validation without flakiness. assertNotEquals("expected at least 1 current segment after translog recovery. segments:\n" + segmentsResponse, 0, numCurrentVersion); }

[github-actions]

✅ Gradle check result for 83fc653: SUCCESS

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 73.33%. Comparing base (59be6ae) to head (83fc653).

Additional details and impacted files

@@             Coverage Diff              @@
##               main   #20747      +/-   ##
============================================
+ Coverage     73.29%   73.33%   +0.04%     
- Complexity    72088    72169      +81     
============================================
  Files          5794     5794              
  Lines        329733   329733              
  Branches      47577    47577              
============================================
+ Hits         241664   241809     +145     
+ Misses        68612    68597      -15     
+ Partials      19457    19327     -130     

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