Test statement containing parent scope variable using Karma

I am testing my controller which has a parent scope variable reference. But it is giving variable undefined error.

subscription (controller)

var vm = this;
var userId=$scope.$parent.vm.userId;
var simId=$scope.$parent.vm.simId;

subscriptionSpec (spec file)

describe('subscription controller',function (){
    var SubscriptionListCtrl,scope;
    beforeEach(module('app'));

    beforeEach(inject(function($controller,$compile,SubscriptionService,dataTableConfigService,commonUtilityService){
    scope={};
    scope.vm={};

    SubscriptionListCtrl=$controller("SubscriptionListCtrl",{$scope:scope,$compile:$compile,SubscriptionService:SubscriptionService,dataTableConfigService:dataTableConfigService,commonUtilityService:commonUtilityService});

    }));
});

Karma Jasmine Error

TypeError: Cannot read property 'vm' of undefined

This comes because of the controller statement

var userId=$scope.$parent.vm.userId;

Also if I replace the $scope.$parent.vm.userId with actual value then it will not give any error.

How do I write the test case for this line?