Test a simple function in a directive, angular

This is my directive:

angular.module('clientApp')
  .directive('positionDropDowns', function (CommonFactory) {
    return {
      templateUrl: 'template/position-drop-downs/position-drop-downs.html',
      restrict: 'E',
      scope: {
        districtsWithSubObjects: '='
      },
      link: function postLink(scope, element, attrs) {

        scope.hello = function(name){
          return 'hello ' + name;
        }
      }
    };
  });

How do I test the hello function? I tried this:

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

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

  beforeEach(module('template/position-drop-downs/position-drop-downs.html'));

  var element,
    scope;

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

    element = angular.element('<position-drop-downs></position-drop-downs>');

    $rootScope.$digest();
  }));

  it('fn hello', inject(function ($compile) {
    expect(element.scope.hello('john')).toBe("hello john");

  }));
});

I get TypeError: undefined is not a function