System.NoAccessException: Invalid Page Redirection: The page you attempted to access has been blocked due to a redirection to an outside website or an improperly coded link or button. Please contact your salesforce.com Administrator for assistance.

@isTest
public class popupcontroller_Test {

 
    static testmethod void loginflow(){
    List<User> lstusers = new list<User>();
    lstusers = Utility.createUser('Business Admin', 1, 'ab'); 
    system.debug('lstusers######'+lstusers);
        string retURL;
        Test.starttest();
         PageReference pageRef = Page.login;
         Test.setCurrentPage(pageRef); 
        popupcontroller popupControllerClass = new popupcontroller();
        popupControllerClass.openPopup();
        popupControllerClass.Cancel(); 
        popupControllerClass.updateRecord();
        
        lstusers[0].Skip_Login_Flow__c = true;
        update lstusers;
        pageref.getParameters().put('retURL', 'home/home.jsp');
        Auth.SessionManagement.finishLoginFlow(retURL);
        popupControllerClass.openPopup();
        popupControllerClass.CurrentRecord();
        Test.stoptest();
    }
}

String retURL = apexpages.currentpage().getparameters().get('retURL');
 
            return Auth.SessionManagement.finishLoginFlow(retURL);