🛠️ Repo: Increase unit test coverage

[boneskull]

counting our integration tests, our coverage is hovering around 90% at time of writing.

...but if we're just looking at unit test coverage, it's only about 50%. 😬

Two parts to this:

• Set up Mocha to compute unit test coverage in isolation
  Create a script (package-scripts.js) and/or configure nyc (.nycrc) to easily compute unit test coverage

  Don't include stuff that we can't unit test reasonably within the count. If it isn't require'd by anything, that's a hint. If the coverage doesn't stand at about 50%, then too much is getting counted.

  This may necessitate two separate setups for browser and Node.js. Just figure out Node.js for this issue; see 🛠️ Repo: Increase browser coverage #2532 if you want to figure out how to compute browser coverage

• Write moar tests (in test/unit/)