Angular unit test: TypeError: $controller is not a function

am setting up unit test for Angular application build with webpack how ever am getting this error when am running my first simple test.

TypeError: $controller is not a function

The controller code like this :

 (function() {
  'use strict';
    angular
      .module('dpServerV2WebappRev2App.controllers')
      .controller('MainCtrl', MainCtrl);
        MainCtrl.$inject = ['$scope'];
        function MainCtrl($scope) {
          $scope.x = 'x';
      }
    })();

Where the test look like this:

describe('MainCtrl', function () {

  beforeEach(module('dpServerV2WebappRev2App.controllers'));

  var $controller;

  beforeEach(inject(function(_$controller_){
    $controller = _$controller_;
  }));

  describe('$scope.brand', function () {
        it('should match the brand portal name', function () {
            var $scope = {};
            var controller = $controller('MainCtrl', { $scope: $scope });
            expect($scope.x).toEqual('x');
        }); 
    });

});