Convert tests from mocha to jest

[guyellis]

@rwky how do you feel about me converting the tests for this repo from mocha to jest?

The reason that I like jest in this context is because it has "all the things."

One of the patterns that I want to fix in this repo is having mocked code in the target prod code. To get away from that we need to inject this mock from the test into the target code. To do this with mocha we need to either hand-roll it or add another dependency like sinon taking out dev dependencies up to 3. With jest we can drop our dev dependencies for testing down to 1.

(Separately we still need to increase the number of dev dependencies for thing like linting but that's another matter.)

[rwky]

Fine with me, gives me a new framework to learn 👍

[rwky]

When this gets done we could do with test coverage being added so coveralls works.

[guyellis]

@rwky - That comes with Jest.

[rwky]

@guyellis just wondering how you're getting on with this?

[guyellis]

@rwky - sorry - slammed at the moment. Not sure when I'll get to look at this.

[rwky]

No worries it's not critical!

[drayzii]

@guyellis That would be great