Reworking client tests, added more utils for fs testing, failing multipl...

This PR is about adding a bunch of tests for various ways that a client might interact with the server, and making sure the filesystem ends up in a state we expect.

This isn't ready to land yet.
In test code we want exceptions to happen and be noisy.  Also, I am hoping you'll drop this rexolveToJSON and resolveFromJSON code in the websocket-test cleanup.