Testing Angular Controller with 'AS'

I would like to testing my controller, i have used 'controller as' in the app, now i am sh*ting myself over testing.

Controller: (half of my controller)

(function(){
    angular.module('donateApp')
      .controller('MainCtrl', mainCtrl);

    mainCtrl.$inject = ['donateFactory', 'donateService', '$location'];

    function mainCtrl(donateFactory, donateService, $location){
      var vm = this,
        checked = false;

      vm.submitted = false;
      vm.submitingForm = false;
      vm.amounts = [
        5, 10, 25, 50, 100
      ];
      vm.regions = donateService.getRegion();
      vm.states = donateService.getStates();

Testing: 'use strict';

describe('Controller: MainCtrl', function () {

  // load the controller's module
  beforeEach(module('donateApp'));

  var MainCtrl,
    scope;

  // Initialize the controller and a mock scope
  beforeEach(inject(function ($controller, $rootScope) {
    scope = $rootScope.$new();
    MainCtrl = $controller('MainCtrl as ctrl', {
      $scope: scope
    });

    $scope.ctrl = MainCtrl;
  }));

  it('Expect the form start with submitted as false', function () {
    expect(MainCtrl.ctrl.submitted).toBeTruthy();
  })
});

Error message i am getting:

TypeError: 'undefined' is not an object (evaluating 'MainCtrl.ctrl')
    at /Applications/MAMP/htdocs/test/spec/controllers/main.js:22

I know it must be a small fix to make it work... anyone can help?

Thanks heaps