[test] Fix unstable test BatchScannerITCase.testKvSnapshotLease

[Kaixuan-Duan]

Purpose

Linked issue: close #3218

Brief change log

The test BatchScannerITCase.testKvSnapshotLease is flaky because it hardcodes expected snapshot IDs ({0L, 0L, 0L}, {1L, 1L, 1L}) assuming snapshot IDs always start from 0 and increment in lockstep across all buckets.

However, FlussClusterExtension.triggerSnapshot() has a race condition: it calls kvSnapshotManager.triggerSnapshot() which submits the task asynchronously to guardedExecutor, then immediately checks currentSnapshotId(). If the async task hasn't executed yet, the method returns null and skips waiting for that bucket's snapshot. The background snapshot still completes eventually, potentially causing snapshot IDs to diverge from the hardcoded expectations.

The fix replaces all hardcoded snapshot IDs with dynamically computed values based on the actual snapshot IDs returned by admin.getLatestKvSnapshots(). A helper method buildExpectedBucketSnapshots() is introduced to construct the expected Long[] array from the actual consumeBuckets map.

Tests

Since the flakiness is caused by a race condition in snapshot ID assignment, it cannot be reliably reproduced in a single run.

The key verification is that the test no longer relies on hardcoded snapshot IDs — it dynamically reads actual snapshot IDs from the cluster and uses them to construct assertions, making it resilient to any snapshot ID offset caused by async timing.

./mvnw -pl fluss-client -Dtest='BatchScannerITCase.testKvSnapshotLease' -DfailIfNoTests=false test

API and Format

Documentation