Replace JUnit dependency with JUnit Jupiter / JUnit Jupiter Vintage

Problem

• Currently all tests are using JUnit 4 but the intention is to migrate to JUnit Jupiter (aka JUnit 5)
• To make this a smooth transition we can simply replace JUnit 4 dependency with JUnit Jupiter Vintage and JUnit Jupiter to keep running the JUnit 4 tests without any change.

Goal

• Transition to JUnit 5
• Open the migration of the JUnit 4 Tests to JUnit 5 step by step without the need to do this in one go.