[KYLIN-4386] Use LinkedHashMap for a deterministic order in test

• Type: Bug
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Fix Version/s: v3.1.0, v3.0.1
• Component/s: Tools, Build and Test
• Labels: pull-request-available
• Flags: Patch
• Assignee: cpugputpu
• Reporter: cpugputpu
• Created: 25/Feb/20 02:16
• Updated: 31/Jul/20 12:10
• Resolved: 25/Feb/20 08:00

Description

The tests in org.apache.kylin.stream.coordinator.CoordinatorTest#testReassignFailOnStartNew and org.apache.kylin.stream.coordinator.CoordinatorTest#testReassignFailOnStopAndSync will fail when making the following assertions:

assertSame(ClusterStateException.ClusterState.ROLLBACK_FAILED, rune.getClusterState());
assertSame(ClusterStateException.TransactionStep.STOP_AND_SNYC, rune.getTransactionStep());

The failure is reported as follows:

java.lang.Exception: Unexpected exception, expected<org.apache.kylin.stream.coordinator.exception.ClusterStateException>

but was<java.lang.AssertionError>

at org.apache.kylin.stream.coordinator.CoordinatorTest.testReassignFailOnStartNew(CoordinatorTest.java:271)

After my analysis, I find that the root cause is that the variable newAssignMap is a HashMap, which makes no guarantee about the order when iterating in org.apache.kylin.stream.coordinator.Coordinator.doReassign(Coordinator.java:516)

The specification about HashMap says that "this class makes no guarantees as to the order of the map; in particular, it does not guarantee that the order will remain constant over time". The documentation is here for your reference: https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html

 

The fix is to use LinkedHashMap instead of HashMap so that the non-deterministic behaviour is eliminated. It will not affect the performance and can make the tests more stable.

 

Issue Links

• links to: GitHub Pull Request #1119