Upgrade all the tests to Junit 5

[Sauhardstark]

Some of the tests have assertions that have been deprecated and alternative imports are being suggested for it.

So rather than, updating just the assertions, I was thinking that it might be better to upgrade the entire Junit framework.

If we update just the assertions, they might become obsolete soon as well. However, Junit 5 is new and should persist for a while. There are also a number of drill down features in Junit 5 that will enhance the strength of the tests. Please let me know what you think

[neuhalje]

This sounds like a good idea. I have been thinking about this as well.