Hi guys 

I'm wondering if someone can help me i'm quite a newbie developer
I've created a button which is updating a field on the account  using a component and class. I'm having trouble gettting any coverage for my class can anyone tell me where i am going wrong ? 

in my test class i'm getting an error on "    updateBillingAddressPlan.UpdateBill(Acc);
" as it doesn't recognise Acc as a variable. 

Here is my class 

public class updateBillingAddressPlan {

    @AuraEnabled

    public static void UpdateBill(){
      
        list<Account> Acc_list = new list<Account>();

        Acc_list = [select id,Shipping_to_Billing__c from Account Limit 1];

        Account acc =new Account();

       acc.id=Acc_list[0].id;

        acc.Shipping_to_Billing__c=true;

        update acc;

    }

}

Test class 

@isTest

    
  
private class updateBillingAddressPlantest{
   @AuraEnabled
        public static boolean UpdateBill(){
        
        //List<Account> Acc_list = new list<Account>();
        
       // Acc_list = [select id,Shipping_to_Billing__c from Account Limit 1];
      //  system.debug(Acc_list.size());  
        Account acc =new Account();

      // acc.id=Acc_list[0].id;
        acc.name ='test account';
        acc.Siret_Number__c='12345678911111';
        acc.Shipping_to_Billing__c=true;

        insert acc;
        system.debug('inserting account was a success');
        return acc.Shipping_to_Billing__c;
        }
        
        
        static testmethod void doTest(){
        Test.startTest();
        User U = new User();
        U.FirstName = 'Testy';
        U.LastName = 'Tester';
      //  U.CurrencyIsoCode = 'GBP';
        U.Username = 'tester_User@test.com';
        U.email = 'tester@test.com';
        U.Alias = 'tstr';
        U.TimeZoneSidKey = 'Europe/London';
        U.LocaleSidKey ='en_GB';
        U.EmailEncodingKey ='ISO-8859-1';
        U.LanguageLocaleKey = 'en_US';
        U.profileID = '00e1t000000FMFdAAO';
       // U.Annual_Target_New_TCVP__c = 100000;
    //    U.Booked_YTD_New_TCVP__c = 50000;
        Insert U;
        
        System.runAs(U){
            Account Acc = new Account();
           // Acc.recordTypeID = Schema.SObjectType.Account.getRecordTypeInfosByName().get('UK Account').getRecordTypeId();
            Acc.Name = 'Account Testing';
            Acc.Siret_Number__c='12345678923456';
           // Acc.cf_customer_sector__c = 'Public';
        //    Acc.cf_customer_segment__c = 'SMB';
            Acc.cf_customer_vertical__c = 'Finance';
            insert Acc;
            
            Opportunity opp = new Opportunity();
            opp.name = 'Test Opportunity';
         //   opp.Start_Date__c = system.today();
            opp.closeDate = system.today().addDays(1);
            opp.stageName = 'Stage 2: Prospect';
            insert opp;}
            
            updateBillingAddressPlan.UpdateBill(Acc);

          
      
        Test.stopTest();
        
        
        
        
        
        }}