Migrate servicetalk-client-api-internal from jUnit4 to jUnit5

[amitvc]

Motivation:

JUnit 5 leverages features from Java 8 or later, such as lambda functions, making tests more powerful and easier to maintain.
JUnit 5 has added some very useful new features for describing, organizing, and executing tests. For instance, tests get better display names and can be organized hierarchically.
JUnit 5 is organized into multiple libraries, so only the features you need are imported into your project. With build systems such as Maven and Gradle, including the right libraries is easy.
JUnit 5 can use more than one extension at a time, which JUnit 4 could not (only one runner could be used at a time). This means you can easily combine the Spring extension with other extensions (such as your own custom extension).
Modifications:

Unit tests have been migrated from JUnit 4 to JUnit 5
Result:

Module servicetalk-client-api-internal now runs tests using JUnit 5

[idelpivnitskiy]

Thanks for the PR @amitvc!

Please, make sure that the build runs correctly. Currently, quality task failed with:

Execution failed for task ':servicetalk-client-api-internal:pmdTest'.
> 35 PMD rule violations were found. See the report at: file:///home/runner/work/servicetalk/servicetalk/servicetalk-client-api-internal/build/reports/pmd/test.html

[amitvc]

@idelpivnitskiy pushed another revision. Successfully ran ./gradlew --parallel clean quality locally as well as test.

[idelpivnitskiy]

The CI reports:

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':servicetalk-client-api-internal:pmdTest'.
> 35 PMD rule violations were found. See the report at: file:///home/runner/work/servicetalk/servicetalk/servicetalk-client-api-internal/build/reports/pmd/test.html

This happens because CI always cherry-picks changes from PR to the up-to-date main branch. Right before your PR we added a new PMD rule for jUnit5 tests (see #1596). Looks like you branched out before that PR was merged.

Please, merge the main branch into yours or rebase and fix the PMD warnings. Otherwise, PR looks great!

[amitvc]

@idelpivnitskiy thanks for the review. I have merged the main branch into mine. Hopefully, the build will go through. I will work on other packages in the list from the original issue.

[idelpivnitskiy]

@amitvc it was not enough just to merge main into your branch. Merging just gives you up to date version of PMD rules, the same as the CI sees. Now, run:

./gradlew :servicetalk-client-api-internal:build

And make sure it succeeds.

[amitvc]

@idelpivnitskiy thanks for the hint. Indeed when I run on this locally it fails. I am fixing this now.

[bondolo]

Thank you @amitvc !