Reduce number of indices created in ClusterSettingsIT

[andrross]

When the number indices created in this test was sufficiently high, tests would frequently hit this failure at some point when creating a file:

Caused by: java.nio.file.FileSystemException: /var/jenkins/workspace/gradle-check/search/server/build/testrun/internalClusterTest/temp/org.opensearch.cluster.settings.ClusterSettingsIT_129BF1D803EFDA59-001/tempDir-002/node_s0/nodes/0/_state/_a1_Asserting_0.doc: Too many open files
  at org.apache.lucene.tests.mockfile.HandleLimitFS.onOpen(HandleLimitFS.java:67)
  at org.apache.lucene.tests.mockfile.HandleTrackingFS.callOpenHook(HandleTrackingFS.java:82)
  at org.apache.lucene.tests.mockfile.HandleTrackingFS.newOutputStream(HandleTrackingFS.java:163)
  at java.****/java.nio.file.Files.newOutputStream(Files.java:215)

This commit changes the random range from [10, 50] to be a fixed value of 3. This still gets the same coverage without unnecessarily increasing test runtime and introducing flakiness around file handle limits.

Resolves #20652

This flakiness was introduced by #20140

Check List

• Functionality includes testing.

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• server/src/internalClusterTest/java/org/opensearch/cluster/settings/ClusterSettingsIT.java

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🔇 Additional comments (1)

server/src/internalClusterTest/java/org/opensearch/cluster/settings/ClusterSettingsIT.java (1)

573-573: Deterministic loop count looks good.

Line 573 reduces test flakiness without changing the verification flow; this is a sensible, stable adjustment.

---

📝 Walkthrough

Walkthrough

The change makes a flaky test deterministic by replacing a random loop iteration count (10-50 times) with a fixed count of 3 in testWithMultipleIndexCreationAndVerifySettingRegisteredOnce. The test logic and verification flow remain unchanged.

Changes

Cohort / File(s)	Summary
Test Determinism server/src/internalClusterTest/java/org/opensearch/cluster/settings/ClusterSettingsIT.java	Replaced random loop iteration (10-50) with fixed count (3) in testWithMultipleIndexCreationAndVerifySettingRegisteredOnce to eliminate test flakiness and ensure consistent behavior across runs.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

Suggested labels

>test-failure, flaky-test

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely summarizes the main change: reducing the number of indices created in the ClusterSettingsIT test.
Description check	✅ Passed	The PR description is comprehensive, explaining the problem (file handle exhaustion), the solution (reducing indices from [10,50] to fixed 3), and includes issue references and testing confirmation.
Linked Issues check	✅ Passed	The PR directly addresses issue #20652 by fixing the flaky ClusterSettingsIT test through deterministic index creation reduction, eliminating the file handle exhaustion errors.
Out of Scope Changes check	✅ Passed	The change is narrowly scoped to fixing flakiness in testWithMultipleIndexCreationAndVerifySettingRegisteredOnce by adjusting loop iteration count, with no unrelated modifications.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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[jainankitk]

Looks fine to me. The purpose of this test does not require random number causing unnecessary flakiness

[github-actions]

❌ Gradle check result for 173f764: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

[github-actions]

✅ Gradle check result for 173f764: SUCCESS

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 73.26%. Comparing base (6b557db) to head (173f764).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main   #20681      +/-   ##
============================================
- Coverage     73.32%   73.26%   -0.06%     
+ Complexity    72064    71973      -91     
============================================
  Files          5781     5781              
  Lines        329395   329402       +7     
  Branches      47525    47526       +1     
============================================
- Hits         241536   241352     -184     
- Misses        68507    68676     +169     
- Partials      19352    19374      +22     

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