Karma unit test 'undefined' is not a function error

I have a custom directive for checking if values in two input fields are equal to each other (repeat password) which I want to test. It works fine but test fails with this error:

TypeError: 'undefined' is not a function (evaluating 'element.add(tween)')

The directive is very simple and straightforward:

angular.module('fmAppApp')
.directive('valueMatch', function () {
    return {
      require: 'ngModel',
      restrict: 'A',
      link: function postLink(scope, element, attrs, ctrl) {
        var tween = '#' + attrs.valueMatch;
        element.add(tween).on('keyup', function () {
          scope.$apply(function () {
            var v = element.val() === $(tween).val();
            ctrl.$setValidity('valueMatch', v);
          });
        });
   }
 };

});

And here is the spec:

describe('Directive: valueMatch', function () {

  // load the directive's module
  beforeEach(module('fmAppApp'));

  var element, origElement,
    scope;

  beforeEach(inject(function ($rootScope) {
   scope = $rootScope.$new();
  }));

  it('should set change validity state of element depending on value of another element',
    inject(function ($compile) {
      origElement = $compile('<input id="orig">')(scope);
      element = $compile('<input value-match="orig" ng-model="repeat">')(scope);
      scope.$digest();
      expect(element.$valid).toBe(true);
      origElement.val('12345');
      scope.$digest();
      expect(element.$valid).toBe(false);
      element.val('12345');
      expect(element.$valid).toBe(true);
 }));
});

So apparently add() is undefined, right? But why?