controller-test.js

test('it created an Upvote with #createUpvote', function () {
  expect(3);
  var store = App.__container__.lookup('store:main');
  store.scheduleSave = function(context, resolver) {
    ok(1);
  };
  var user = null;
  var story = null;

  Ember.run(function () {
    user = store.createRecord('user');
    story = store.createRecord('story');
  });

  var controller = this.subject({ store: store });

  equal(store.all('upvote').get('length'), 0, "No upvotes have been saved");

  Ember.run(function () {
    controller.createUpvote(story, user);
  });

  equal(store.all('upvote').get('length'), 1, "An upvote is created");
});

controller.js

import Ember from 'ember';

export default Ember.ObjectController.extend({
  createUpvote: function (story, user) {
    this.store.createRecord('upvote', {
      story: story,
      user: user
    }).save();
  }
});