Handle internal error checks/failure assertions differently

[plocket]

To test that our users' tests fail correctly (and thus pass our tests on the Scenario level while failing on the Step level), we're modifying properties of scenario in After(). In the slack channel, cucumber is discussing making that object immutable or something like that. This comment starts that discussion.

We need a different way to pass our correctly failing tests. Another repo integrating nightwatch has been dealing with this too. I've been pointed at this file.

These are actually cucumber tests that nest their lib's tests in a sub process. So they're testing their cucumber tests with another, outer, set of cucumber tests. The outer tests make sure the correct failures happen. We can try to use the same method, though I haven't read deeply enough to truly understand how to set it up.