100% coverage not acheived error in challenge

public class AccountProcessor {
  @future
  public static void countContacts(List<Id> accountIds) {
    List<Account> accounts = [Select Id, Name from Account Where Id IN :accountIds];
    // process account records to do awesome stuff
    List<Contact> con = [select id from contact where AccountId in :accounts];
        for(Account a : accounts){
            a.Number_Of_Contacts__c=con.size();
        }
  }
}

@isTest
public class AccountProcessorTest {
    public static testmethod void TestAccountProcessorTest() {
   Account a= new Account ();
        a.Name='Test Account';
        Insert a;
        Contact cont=New Contact();
        cont.FirstName='Bob';
        cont.LastName='Masters';
        cont.AccountId=a.ID;
        Insert cont;
        List<Id> setAccId = new List<ID>();
        setAccId.add(a.id);
        Test.startTest();
      AccountProcessor.countContacts(setAccId);
    Test.stopTest();
        Account ACC = [select Number_of_Contacts__c from Account where id = :a.id LIMIT 1];
        System.assertEquals ( Integer.valueOf(ACC.Number_of_Contacts__c) ,1);
}
    }