Fix failing tests, upgrade to should 4.0

When I tried to clone the repo and run the tests, 9 of them were failing. Needless to say, it's a little unsettling to use a testing framework with failing tests.

I fixed the failing tests and upgraded the `should` dev dependency to 4.0. Seems the tests were failing because they were looking for properties on should's `Assertion` object that were not present, namely `status` and `include`.