NIFI-8356: Add unit test for LongRunningTaskMonitor.

[turcsanyip]

https://issues.apache.org/jira/browse/NIFI-8356

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[exceptionfactory]

Thanks for adding the unit test @turcsanyip! This covers all the bases, but what do you think about simplifying it to verify calling EventReporter and leave out verification of logging? That seems to be a good balance of verification without expecting specific logging statements.

[exceptionfactory]

Is it necessary to introduce testing for log statements? Testing the invocation of EventReport.reportEvent() seems sufficient since that is the primary purpose of the monitor. Avoiding evaluating of logging in the unit test removes the need for exposing these methods for testing purposes.

[turcsanyip]

The main purpose of this class to log info about long running (possible stuck) tasks in the nifi log file to make troubleshooting easier. The nifi log is the only persistent storage of these messages because the bulletins disappear after a while. That's why I would assert these statements.

Additionally, the messages are shown on the UI in two places: controller and processor level bulletins. EventReport.reportEvent() handles the controller level bulletin but the processor level bulletin is triggered by log items written by the processors logger. That's why we need assert that log call.

Asserting the last "Active threads:" summary log may be unnecessary but after checking the other logs I added it too.

[exceptionfactory]

Thanks for the explanation @turcsanyip, that makes sense.

[exceptionfactory]

+1 Thanks @turcsanyip!