a simple ember example showing how to select multiple items in a "multi select" (integration testing)

ember-integration-test-with-multi-select.js

test('multi select in a ember integration test', function(assert) {
  //setup your model and other component state ...
  this.render(hbs`{{my-multi-select model=model options=options}}`);
  this.$('.some-multi-select > option[value="' + MY_NEW_ID + '"]').prop('selected',true).trigger('change');
  assert.equal(model.get('related_things').get('length'), new_count_with_added_item);
});