[FLINK-29452] Allow unit tests to be executed independently

[RyanSkraba]

What is the purpose of the change

This is a minor clean up of the unit tests that check the functionality of @RetryOnFailure and @RetryOnException. Currently, executing a single test method will fail; all unit tests in these two classes need to be executed in order for any to pass.

Brief change log

• The current strategy is to count the number of times a method was called in a static int variable, and checking that every test was run the expected number of times in an @AfterAll verification.
• The new strategy is to count the number of times any test method was called in a single hashmap (using the @BeforeEach and TestInfo from JUnit5), and verify the counts only if they exist in the @AfterAll
• Rename NUMBER_OF_RUNS to NUMBER_OF_RETRIES which is a bit clearer.
• Additional hotfix: I noticed a missing space padding in one of the messages.

Verifying this change

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

One way to check this manually is to run any single test in isolation:

(
  cd flink-test-utils-parent/flink-test-utils-junit/ && 
    mvn test -Dtest=org.apache.flink.testutils.junit.RetryOnExceptionExtensionTest#testSuccessfulTest
)

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: no
• The runtime per-record code paths (performance sensitive): no
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn, ZooKeeper: no
• The S3 file system connector: no

Documentation

• Does this pull request introduce a new feature? no
• If yes, how is the feature documented? not applicable

[flinkbot]

CI report:

• bd29f34 Azure: SUCCESS

Bot commands

The @flinkbot bot supports the following commands:

• @flinkbot run azure re-run the last Azure build

[RyanSkraba]

Hello! I've rebased this PR to master. I don't believe there are any remaining requested changes that I haven't addressed (by comment or other).

I will be mostly away from my computer for a couple of weeks, but I'll check in if anything changes!

[RyanSkraba]

OK, change applied, thanks for the review

[XComp]

Thanks for updating the PR. There are still some plain text method names in the test code which we could get rid off.

Additionally, can you reorganize/squash the commits and rebase the branch to prepare the final CI run?

[XComp]

LGTM 👍 Thanks for addressing my comments. Please squash the commits into reasonable chunks to prepare the PR merge.

[RyanSkraba]

Rebased and squashed!