HDDS-16170. Intermittent failure in TestSnapshotDiffManager#testLoadJobsOnStartUp

[smengcl]

Generated-by: Claude Code (Opus 4.8)

What changes were proposed in this pull request?

TestSnapshotDiffManager#testLoadJobsOnStartUp fails intermittently with expected: <DONE> but was: <IN_PROGRESS>.

The test stubs generateSnapshotDiffReport with a doAnswer that writes DONE to the DB inside the answer body, calls loadJobsOnStartUp(), then waits with attempt(() -> verify(spy, atLeast(1)).generateSnapshotDiffReport(...)) before reading the job back and asserting DONE.

Mockito records an invocation before it runs the stubbed answer, so the verify(...) wait can pass as soon as the worker thread enters generateSnapshotDiffReport, while the answer is still running and has not yet persisted DONE. The main thread then reads the job and observes the original IN_PROGRESS, so the assertion fails.

The fix waits on the actual observable end state the test asserts: it polls getSnapshotDiffJobFromDb(...).getStatus() until it is DONE, instead of waiting on the Mockito invocation. This is deterministic by construction because the read the assertion depends on is exactly what is waited on. No production code changes.

What is the link to the Apache JIRA

https://issues.apache.org/jira/browse/HDDS-16170

How was this patch tested?

Ran the affected test locally against the change:

mvn -pl :ozone-manager -am test -Dtest='TestSnapshotDiffManager#testLoadJobsOnStartUp' -DskipShade -DskipRecon -DskipDocs -Dsurefire.failIfNoSpecifiedTests=false

A single green run cannot prove non-flakiness, so the fix is made deterministic by construction: the wait polls the same persisted job status that the subsequent assertion reads, closing the window between Mockito recording the invocation and the stubbed answer writing DONE to the DB.

[Copilot]

Pull request overview

This PR fixes an intermittent failure in TestSnapshotDiffManager#testLoadJobsOnStartUp by changing the test’s synchronization strategy to wait on the persisted job status rather than a Mockito invocation, eliminating a race between method entry and the stubbed doAnswer completing its DB write.

Changes:

• Replace attempt(verify(...)) with polling of getSnapshotDiffJobFromDb(...).getStatus() until it reaches DONE.
• Add explanatory comments documenting why Mockito-based waiting was flaky in this scenario.

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