[fix][test] Fix flaky TopicListSizeResultCacheTest concurrent requests test

[merlimat]

Flaky test failure

java.lang.AssertionError: expected [true] but found [false]
	at org.testng.Assert.assertTrue(Assert.java:56)
	at org.apache.pulsar.broker.topiclistlimit.TopicListSizeResultCacheTest.testResultHolder_concurrentRequestsWaitForFirstToComplete(TopicListSizeResultCacheTest.java:132)

Summary

Fix flaky TopicListSizeResultCacheTest.testResultHolder_concurrentRequestsWaitForFirstToComplete which had two bugs:

1. Unsynchronized ArrayList: futures list was populated from multiple threads via futures.add() without synchronization, causing potential data corruption and lost adds.

2. Wrong ordering assumption: The test assumed futures.get(0) was the "first" request (the one that wins the CAS in getSizeAsync() and gets back a completed future). But thread scheduling is nondeterministic — any thread could add its future to the list first regardless of which called getSizeAsync() first.

Fix

• Use CopyOnWriteArrayList for thread-safe concurrent adds
• Instead of assuming futures.get(0) is the CAS winner, count how many futures are done (should be exactly 1) and find it via stream().filter(isDone)
• Verify all futures complete after updateSize() without assuming index-based ordering

Verified with invocationCount = 100 — 100/100 pass.

Documentation

• doc-not-needed
  (Your PR doesn't need any doc update)

Matching PR in forked repository

No response

Tip

Add the labels ready-to-test and area/test to trigger the CI.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 14 lines in your changes missing coverage. Please review.
✅ Project coverage is 72.72%. Comparing base (7f6bc23) to head (be63377).
⚠️ Report is 8 commits behind head on master.

Files with missing lines	Patch %	Lines
...r/topiclistlimit/TopicListSizeResultCacheTest.java	0.00%	14 Missing ⚠️

Additional details and impacted files

@@              Coverage Diff              @@
##             master   #25357       +/-   ##
=============================================
+ Coverage     37.45%   72.72%   +35.26%     
- Complexity    13161    34253    +21092     
=============================================
  Files          1897     1954       +57     
  Lines        150557   154770     +4213     
  Branches      17215    17718      +503     
=============================================
+ Hits          56398   112550    +56152     
+ Misses        86428    33182    -53246     
- Partials       7731     9038     +1307     

Flag	Coverage Δ
inttests	25.77% <0.00%> (-0.27%)	⬇️
systests	22.50% <0.00%> (+<0.01%)	⬆️
unittests	73.71% <ø> (+39.53%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...r/topiclistlimit/TopicListSizeResultCacheTest.java	0.00% <0.00%> (ø)

... and 1419 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[lhotari]

LGTM