[FLINK-8160]Extend OperatorHarness to expose...

[wangtuo21]

...metricsGroup

What is the purpose of the change

To better test interactions between operators and metrics the harness should expose the metrics registered by the operator.

Brief change log

add method getMetricGroup() to class AbstractStreamOperatorTestHarness

Verifying this change

This change is a trivial rework / code cleanup without any test coverage.

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): no
• The public API, i.e., is any changed class annotated with @Public(Evolving): no
• The serializers: (yes / no / don't know)
• The runtime per-record code paths (performance sensitive): no
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Yarn/Mesos, ZooKeeper: no

Documentation

• Does this pull request introduce a new feature? no

[zentol]

Please explain how this solution allows the user of a AbstractStreamOperatorTestHarness to access the metrics registered by the contained operator.

[wangtuo21]

@zentol , I misunderstood the request. Does it go in the right direction now? Thank you

[zentol]

No, this still doesn't work.

The MetricGroup you're trying to expose is created in AbstractStreamOperator#setup. However, the parent MetricGroup retrieved through Environment#getMetricGroup is null since this method is never mocked for the MockEnvironment in AbstractStreamOperatorTestHarness. Thus, in AbstractStreamOperator#setup we're entering the fail-safe block which creates a dummy MetricGroup that never stores anything.
As such no metric can actually be retrieved from the MetricGroup.

Please, ask questions if you don't know to fix an issue or verify the fix. And at the very least try it out once, otherwise you're just wasting the committers' time.

For a proper solution you have to create a TaskMetricGroup in the AbstractStreamOperatorTestHarness, which you then use in the MockEnvironment by returning it from Environment#getMetricGroup
With this scheme however metrics are only available while the task hasn't been closed (as metrics are cleaned up), so for better usability your TaskMetricGroup must override TaskMetricGroup#getOperator to return a special OperatorMetricGroup that also stores registered metrics in the AbstractStreamOperatorTestHarness. We do not store them indefinitely in the OperatorMetricGroup since that would change one of the core behaviors of the MetricGroup. Finally, add a getMetrics method to the AbstractStreamOperatorTestHarness to actually access registered metrics.