♻️ Refactor: Migrated the test logic out to Abstract class

By migrating the test logic out into an Abstract class, that class can
be directly copied from one project to another.

This will allow me to create/debug tests in one project (say the Jersey
project) and then copy that test class directly to the Spring Boot
autoconfiguration project.

Ideally, the class could be shared in a neutral place, but copying is
good enough for now.

Author: rmcdouga