KAFKA-15610: Fix CoreUtils.swallow() test gaps

[ghostspiders]

The CoreUtils.swallow() method in different logging levels test.

[ghostspiders]

Hi, @divijvaidya please review this

[divijvaidya]

There is a previous PR open for this at https://github.com/apache/kafka/pull/14583

I have a comment there on possible usage of spy. Can you please explore that approach and let us know why it might or might not be feasible.

[ghostspiders]

@divijvaidya I am using Mockito's verify to test CoreUtils.swallow(), but I am encountering an 'Argument(s) are different! Wanted:' error because the parameter is a function. I currently do not have a good solution for this issue.

[chia7712]

@ghostspiders Do you have jira account?