userinfo.getuserid() returning null in test class

I have a test class which inserts partner user for testing. So, when I pass userinfor.getuserID(), it is returning null due to which my test class is failing with error

"System.NullPointerException: Attempt to de-reference a null object"

Below is the test class:

   @isTest (seeAllData=False)
private class KC_Reg_Handler_Test {
     @isTest (seeAllData=true)
    static void testPDRegistration() {
        Account acct = testDataGenerator.createTestAccount(); 
        update acct;
        Contact cont = testDataGenerator.createTestContact();

        String uniqueName = 'xyz@account.999888777.com';
        Auth.UserData dataX = new Auth.UserData('identifier', 'firstName', 'lastName', 'fullName', 'cat@gmail.com', 
            null, uniqueName, 'en', 'provider', null, null);

        Test.startTest();
        // PD Auth Provider Testing
        KC_RegHandler authP = new KC_RegHandler();
        User usr = authP.createUser(UserInfo.getUserId(), dataX);
        authP.updateUser(null, null, dataX);       

        // PD User Provisioning Web Service
        RestRequest req = new RestRequest(); 
        RestResponse res = new RestResponse();
        req.requestURI = 'https://' + URL.getSalesforceBaseUrl().getHost() + '/services/apexrest/PD_AccountWS/0010';
        req.httpMethod = 'POST';
        RestContext.request = req;
        RestContext.response = res;

        PD_UserAccountWS.PD_UserAccountRequest pupr = new PD_UserAccountWS.PD_UserAccountRequest();
        pupr.Accountid = '111222333444';
        pupr.emailAddress = 'cat@mat.com';
        pupr.firstName = 'John';
        pupr.lastName = 'Account';
        pupr.language = 'en_US';
        PD_UserAccountWS.PD_UserAccountResponse upws = PD_UserAccountWS.doPost(pupr);

        pupr.Accountid = '111222333445';
        upws = PD_UserAccountWS.doPost(pupr);
        upws = PD_UserAccountWS.doPost(pupr);
        //
        req.httpMethod = 'GET';
        upws = PD_UserAccountWS.doGet();

        req.requestURI = 'https://' + URL.getSalesforceBaseUrl().getHost() + '/services/apexrest/PD_AccountWS';
        req.httpMethod = 'POST';
        RestContext.request = req;
        RestContext.response = res;
        upws = PD_UserAccountWS.doPost(pupr);
        req.httpMethod = 'GET';
        upws = PD_UserAccountWS.doGet();

        Test.stopTest();
    }



       @isTest (seeAllData=true)
    static void testPDRegistrationLocaleLangCheckErr() {
        Account acct = testDataGenerator.createTestAccount();                 
        Contact cont = testDataGenerator.createTestContact();

        String uniqueName = 'xyz@account.999888777.com';

        Auth.UserData dataX = new Auth.UserData('badidentifier', 'firstName', 'lastName', 'fullName', 'cat@gmail.com', 
            null, uniqueName, 'en', 'provider', null, null);

        Test.startTest();
        KC_RegHandler authP = new KC_RegHandler();    

        String provReq = '{"firstName": "Hugh", "lastName": "Man", "emailAddress": "abc@xyz.com", "language": "en_US", "locale": "en_US", "alias": null, "timeZone": null}';
        acct.Provision_Request__c = provReq;
        acct.Provision_Status__c = 'Active';

        update acct;
        User temp = authP.createUser(UserInfo.getUserId(), dataX); 
        system.debug('dataX'+dataX);
        system.debug('UserInfo.getUserId()'+UserInfo.getUserId());
        system.debug('temp'+temp) ;      
        User badLocaleLang = [SELECT Id, languagelocalekey, localesidkey, Contact.Account.Account_Request__c FROM User WHERE Id=:temp.Id LIMIT 1];
        system.debug('badLocaleLang '+badLocaleLang );        
        System.assertEquals(badLocaleLang.Contact.Account.Account_Request__c, provReq);
        System.assertEquals(badLocaleLang.languagelocalekey, 'en_US');
        System.assertEquals(badLocaleLang.localesidkey, 'en_US');

        Test.stopTest();
    }

}

Below is the createUser Method from Reg handler class

global User createUser(Id portalId, Auth.UserData data){
        if(!canCreateUser(data)) {
            //Returning null or throwing an exception fails the SSO flow
            return null;
        }
        User impersonatorUser = verifyImpersonator(data);
        if(impersonatorUser != null) {
            return impersonatorUser;
        }
        // Check if User is already present with Google Id
        list<User> usrList = [select Id from User where Contact.Account.Account_Id__c = :data.username and Contact.Account.Account_Status__c = 'Active' ORDER BY lastmodifieddate desc limit 1];
        if(usrList != null && usrList.size() > 0) {
            return usrList[0];
        }
        else {
            System.debug('IDX = ' + data.username);
            //The user is authorized, so create their Salesforce user
            list<Contact> con = [select Id, AccountId, Account.Account_Id_Format__c, Account.Account_Request__c from Contact 
                where Account.Account_Id__c =:data.username and Account.Account_Status__c = 'Active' limit 1];
            if(con != null && con.size() > 0) {
                User u = new User();
                Profile p = [SELECT Id FROM profile WHERE name='Paid Account'];


                String emailUser = data.email.split('@')[0];
                String emailDomain = data.email.split('@')[1];

                //TODO: Customize the username. Also check that the username doesn't already exist and
                //possibly ensure there are enough org licenses to create a user. Must be 80 characters or less.
                u.username = data.email;
                u.email = data.email;
                u.lastName = data.lastName;
                u.firstName = data.firstName;
                String alias = emailUser;
                //Alias must be 8 characters or less
                if(alias.length() > 8) {
                    alias = alias.substring(0, 8);
                }
                u.alias = alias;
                u.languagelocalekey = UserInfo.getLocale();
                u.localesidkey = UserInfo.getLocale();
                u.emailEncodingKey = 'UTF-8';
                u.timeZoneSidKey = 'America/Phoenix';
                u.profileId = p.Id;
                u.ContactId = con[0].Id;
                u.IsActive = true;
                u.CompanyName = 'Custom User';
                u.UserPreferencesHideS1BrowserUI = true;


                return u;
            }


        }
    }

Below is the stack trace

Class.KC_Reg_Handler_Test.testPDRegistrationLocaleLangCheckErr: line 87, column 1

I found that the issue is with userinfo.getuserid() and it is returning null value while inserting the user. Can anyone help me with it.