Upgrade tests to run with JUnit5

[strangelookingnerd]

• removed JUnit4 dependency
• migrated namespaces

Testing done

mvn clean verify runs without problems.

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1. Make sure you are opening from a topic/feature/bugfix branch (right side) and not your main branch!
2. Ensure that the pull request title represents the desired changelog entry
3. Please describe what you did
4. Link to relevant issues in GitHub or Jira
5. Link to relevant pull requests, esp. upstream and downstream changes
6. Ensure you have provided tests - that demonstrates feature works or fixes the issue

[MarkEWaite]

Changes look good to me. I compared the JaCoCo coverage report before and after and the change does not reduce coverage. Thanks!

[MarkEWaite]

I labeled the issue as a test (test improvement task) so that it would be classified by release drafter under one of the common headings in the changelog. You're welcome to assign it a different label if you prefer something else