Unit Test Cases: cleanup, static imports for Assertions

[LaFriska]

Pull Request Etiquette

• [x] I have checked the PRs for upcoming features/bug fixes.
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Changes

• [ ] Internal code
• [ ] Library interface (affecting end-user code)
• [ ] Documentation
• [x] Other: Unit Test Cases

Closes Issue: NaN

Description

I have noticed an overwhelming amount of Assertions.assertEquals(), Assertions.assertTrue() or other similar static method calls from the Assertions class. I also noticed that some test classes have static imports for Assertions, and some don't. I decided to clean up the code by adding static imports for Assertions for the classes that did not import them already.

Another minor change I made within the code cleanup was that I extracted out a huge builder chain into a separate private method in MessageSerializationTest, to ensure code tidiness.