While analyzing HDFS-17951, I found that many tests leak mini-cluster instances (MiniDFSCluster, MiniQJMHACluster, MiniJournalCluster, MiniRouterDFSCluster, MiniYARNCluster, MiniMRYarnCluster and variants).
A static scan of the test sources — vetted by hand to remove false positives such as clusters owned by harnesses or torn down through wrapper objects — found 86 cases in ~60 files, in three categories: A) 27 tests create a local cluster and never shut it down on any path. B) 38 tests shut the cluster down only on the happy path (no finally / try-with-resources), so the cluster leaks exactly when the test fails. C) 21 classes hold a cluster in a field with no teardown in the class or its superclasses. Impact: leaks stay within the class, but a leaked cluster keeps CI resources under the remaining tests, and one failure can cascade into bogus failures of later tests in the class.There is no impact on production, only improvement for CI testing. Please open a JIRA for this, and I will be happy to contribute. Regards, Jose Luis López
