Consider upgrading to JUnit 5 (Do not need to migrate all tests at once)

[techsy730]

One of JUnit 5's big wins is the ability to run tests in parallel. Given the large amount of tests we have, this would be a major time win.

Thankfully we can take our time with refactoring the tests to JUnit 5 APIs, as the JUnit 5 Vintage module allows running native JUnit 4 tests in the JUnit 5 framework.