update tests to use JUnit 5

[lachlan-roberts]

trafficstars

Currently the tests use junit 4.13.2, this should be upgraded to JUnit 5 at some point which has an updated API with better functionality.

Specifically this would be useful for the runtime-test module where we use parameterized tests.

[ludoch]

need to see the impact on internal google3 build and the version it uses...