[fix][test] Fix flaky IsolatedBookieEnsemblePlacementPolicyTest.testMetadataStoreCases

[merlimat]

Motivation

IsolatedBookieEnsemblePlacementPolicyTest.testMetadataStoreCases is flaky because it uses Thread.sleep-based timing to control when CompletableFutures complete. On fast machines, the background thread can complete earlier than expected, causing getExcludedBookiesWithIsolationGroups to see the updated cache value before the test expects it.

Stack trace

IsolatedBookieEnsemblePlacementPolicyTest > testMetadataStoreCases FAILED
    java.lang.AssertionError: expected [true] but found [false]
        at org.testng.Assert.fail(Assert.java:110)
        at org.testng.Assert.failNotEquals(Assert.java:1577)
        at org.testng.Assert.assertTrue(Assert.java:56)
        at org.testng.Assert.assertTrue(Assert.java:66)
        at IsolatedBookieEnsemblePlacementPolicyTest.testMetadataStoreCases(IsolatedBookieEnsemblePlacementPolicyTest.java:212)

Modifications

Replace the Thread.sleep-based timing with manually-controlled CompletableFuture completion at the exact test points where the futures should transition from pending to complete. This eliminates the timing race entirely.

Documentation

• doc-not-needed