Overhaul tests to use Jest

[jjnesbitt]

Original comment: #11 (comment)

This should take advantage of Jest's ability to provide creation/teardown logic for each test, in order to create/teardown a new workspace to be used for each test.

After this is done, the test referenced in the comment above should be added.

[waxlamp]

@AlmightyYakob, looks like we had already filed this and assigned to Mike V. I've reassigned to you but it's low priority for the moment.