This should be:
`'required' => array(array('nonexistent_field', 'other_missing_field')),`

Because the first argument is an array of fields that are required.

This seems like it should solve it, but what's happening in the failing test is that the bulk rules are getting parsed as - even with the array change:

`$this->rule('required', 'nonexistent_field', 'other_missing_field')`

Instead of this (which is correct):

`$this->rule('required', array('nonexistent_field', 'other_missing_field'))`

Fix that parsing issue, and the test should pass.