K14130: Reduce RackAwarenesssTest to unit Test

[guozhangwang]

While working on KAFKA-13877, I feel it's an overkill to introduce the whole test class as an integration test, since all we need is to just test the assignor itself which could be a unit test. Running this suite with 9+ instances takes long time and is still vulnerable to all kinds of timing based flakiness. A better choice is to reduce it as a unit test, similar to HighAvailabilityStreamsPartitionAssignorTest that just test the behavior of the assignor itself, rather than creating many instances hence depend on various timing bombs to not explode.

Since we mock everything, there's no flakiness anymore. Plus we greatly reduced the test runtime (on my local machine, the old integration takes about 35 secs to run the whole suite, while the new one take 20ms on average).

Committer Checklist (excluded from commit message)

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

[guozhangwang]

ping @vvcephei for a quick review.

[divijvaidya]

We are actively trying to get rid of EasyMock/PowerMock from all classes. Please use Mockito in this new code.

Here are a couple of helpful tips that you might useful:

1. EasyMock.createNiceMock/EasyMock.createMock can be replaced with mock from Mockito. All mocks in Mockito are nice.
2. Mockito doesn't require replay so you can get rid of those lines completely.
3. You might want to consider running the test using @RunWith(MockitoJUnitRunner.StrictStubs.class) since it comes with a lot of benefits highlighted in the docs https://javadoc.io/doc/org.mockito/mockito-core/latest/org/mockito/junit/MockitoJUnitRunner.html

[guozhangwang]

Thanks @divijvaidya , I've updated the class to switch to mockito.

[dplavcic]

[optional]

@guozhangwang, if you add @RunWith(MockitoJUnitRunner.StrictStubs.class) at class level and re-run all tests you will see following exception (or warning, it depends on how you look at it):

Unnecessary stubbings detected in test class: RackAwarenessStreamsPartitionAssignorTest
Clean & maintainable test code requires zero unnecessary code.
Following stubbings are unnecessary (click to navigate to relevant line of code):
  1. -> at org.apache.kafka.streams.processor.internals.RackAwarenessStreamsPartitionAssignorTest.createMockTaskManager(RackAwarenessStreamsPartitionAssignorTest.java:173)
Please remove unnecessary stubbings or use 'lenient' strictness. More info: javadoc for UnnecessaryStubbingException class.

To read more about MockitoJunitRunner please check the official docs at: https://javadoc.io/doc/org.mockito/mockito-core/latest/org/mockito/junit/MockitoJUnitRunner.html

[guozhangwang]

I'm merging in this PR now since it includes a hotfix on [StreamTaskTest.java] to turn the build to green.