What does this implement/fix? Explain your changes.

Since the embedded unit tests have been patched we can re-upgrade to NUnit3 from @filmor .

Does this close any currently open issues?

N/A

Any other comments?

On v.2.x of NUnit I'm noticing that the tests finish and hang for ~40 seconds before releasing control. on v3.x it gives some warnings but I'm not sure if thats related.

Personally I'm indifferent to prefer v2.x since it released control and occasionally print the traceback that was key to figuring the old problem out. But since that looks to be solved, I don't have a strong argument.