Modify input field value via simulated keypress in Karma

Using Karma + PhantomJS, I'm testing an Angular directive that involves form fields. I need to trigger keypress events on an input field so that the value, $dirty, and $valid scope values are properly set.

Keypress events don't appear to actually change the value or validation settings, they.

If there's no way to simulate entry, is there a way I can manually trigger the dirty flag, and validation checks (after setting the value).

These tests are for individual components and are separate from what we're using Protractor to test.