Test an application using JUnit 4

[aguibert]

User story:

As a user of this test framework, I want to test my application using JUnit 4 because I already have significant investment in JUnit 4 and do not wish to migrate to JUnit Jupiter.

Additional detail:

JUnit Jupiter is the newest version of JUnit and has a good amount of adoption. From a test framework implementor perspective, Jupiter is far more flexible and powerful than previous versions of JUnit. By default, we will use Jupiter in implementation and examples, but it should also be possible for users to use JUnit 4 (although it may be a bit clunkier).

[appiepollo14]

@aguibert as junit5 is the de facto standard nowadays, is this issue still relevant for you?