KAFKA-10083: fix failed testReassignmentWithRandomSubscriptionsAndChanges tests

[showuon]

The failed test is because we changed the class member partitionMovements initialization to when the class instance created, from initialized when used within assign method. This won't have any issue when 1st used the AbstractStickyAssignor instance. But if it is used later, the partitionMovements will store the old info, and cause this failed tests. Fix it by moving the partitionMovements initialization back to assign method.

Committer Checklist (excluded from commit message)

• Verify design and implementation
• Verify test coverage and CI build status
• Verify documentation (including upgrade notes)

[showuon]

@ableegoldman , could you review this PR to fix the failed tests? Thanks.

[ableegoldman]

Can we still initialize it here as well? I remember that was necessary for some tests to pass since they might never get to the generalAssign method and isSticky would hit NPE

On the other hand, it seems like isSticky is pointless to call unless we get to the generalAssign method. So maybe we should just remove that from the tests that only do the constrainedAssign and just verify the stickiness directly?

[ableegoldman]

cc @mjsax @guozhangwang , should be cherrypicked to 2.6, 2.5, and 2.4 (once my comment above is addressed)

[ijuma]

ok to test

[ableegoldman]

Hey @showuon, this failing test has been blocking others so I submitted a quick PR to fix it ASAP: #8786

But as noted in the PR and in my earlier comment here, this is just the "minimum fix". I think ideally we would improve the tests to not just rely on PartitionMovements/#isSticky for stickiness verification. If you're interested in pivoting this PR to work on that, I'd be happy to review it!

[showuon]

Close this PR since it'll be fixed in #8786. And #8788 will do the test improvement. Thanks.