Ember CLI Testing with ic-ajax

I'm having trouble acceptance testing an Ember CLI Component that uses ic-ajax to submit a form.

The problem is that the andThen function in the acceptance test doesn't wait for the form submission to resolve.

Component:

import Ember from 'ember';
import ajax from 'ic-ajax';

export default Ember.Component.extend({
  tagName: 'form',

  // ...snip...

  submit(e) {
    e.preventDefault();

    const request = ajax({
      url: "url.com"
    });
    // Debugging in test mode, Ember.Test.lastPromise === null here?
  }

  // ...snip...

});

Acceptance Test:

test('it surfaces errors', function(assert) {
  visit('/test');
  let component;

  andThen(function() {
    component = find('.my-form');

    fillIn('input[Placeholder="Email"]', 'not@valid');
    click('button[type="submit"]');    

    andThen(function() {
      // PROBLEM: This code doesn't wait for the ic-ajax promise to resolve
      assert.ok(component.hasClass('error'), "The component applied the error classname.");
    });
  });
});

Creating the ic-ajax promise doesn't seem to set Ember.Test.lastPromise, meaning andThen doesn't wait for the form submit to return.

Am I missing something here?