KAFKA-14747: record discarded FK join subscription responses

[AyoubOm]

As described in KAFKA-14747, we are not recording discarded FK join responses in case of receiving a join response for an old record (whose hash value has changed in the left table). This PR adds the record to dropped records sensor

Committer Checklist (excluded from commit message)

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

[AyoubOm]

@mjsax Please have a look when you have some time

[AyoubOm]

Thanks for the PR! Overall LGTM, but we should add a unit test for the newly added sensor.

Thanks @mjsax for your review. I added tests of the dropped record sensor (I believed we didn't have access to metrics from the context but we have indeed).

Another point, I think there are some missing tests in the foreignkeyjoin package, and problems in naming a test class. For example, ForeignTableJoinProcessorSupplierTest is not testing ForeignTableJoinProcessorSupplier but SubscriptionJoinProcessorSupplier. Hence, I think the ForeignTableJoinProcessorSupplier is not tested.

[mjsax]

Another point, I think there are some missing tests in the foreignkeyjoin package, and problems in naming a test class. For example, ForeignTableJoinProcessorSupplierTest is not testing ForeignTableJoinProcessorSupplier but SubscriptionJoinProcessorSupplier. Hence, I think the ForeignTableJoinProcessorSupplier is not tested.

Thanks for pointing this out. Would you like to do a follow up PR and rename the test? And maybe also close this test gap (of not, we can also just file a ticket for this for now.)

[mjsax]

Also, thanks for the PR! Merged to trunk.

[AyoubOm]

Another point, I think there are some missing tests in the foreignkeyjoin package, and problems in naming a test class. For example, ForeignTableJoinProcessorSupplierTest is not testing ForeignTableJoinProcessorSupplier but SubscriptionJoinProcessorSupplier. Hence, I think the ForeignTableJoinProcessorSupplier is not tested.

Thanks for pointing this out. Would you like to do a follow up PR and rename the test? And maybe also close this test gap (of not, we can also just file a ticket for this for now.)

Sure, I will look into that.