Basic implementation of real unit tests using sinon & sinon-chai

I chose what used to be called setupWebSocketServer to be the unit of code under test for which to write some true unit tests that would give us an example of things exercising sinon and sinon-chai.  Not terribly surprisingly, that code wasn't very unit-testable as written, so this forced a bit of refactoring there.

There's a bit of a learning curve here, but I expect just the presence of these tests in the tree to should act as good examples of how to work with it meaningfully.

Requesting review from at least @tOkeshu; getting additional review from @n1k0 would make me pretty happy, but I don't want to overload him or block on that, so I'll leave that at his discretion.  Comments from everyone are, of course, welcome.