public class AccountProcessor {
    
	@future
    public static void countContacts(List<Id> AccIds){
        
    List<Account> acctsContacts = new List<Account>();
        
    //List<Contact> noOfContacts = new List<Contact>();
        
        //integer noOfContacts;
        
    for(ID accn: AccIds){
            
     //contactsID = [Select ID from Contact where Account.ID = :accn];
            
     //noOfContacts = [Select COUNT() from Contact where Account.ID = :accn];
          
     	acctsContacts =  [Select Name, (Select Firstname, Lastname FROM Contacts)
                          FROM Account
                          WHERE ID =:accn]; 
         
            for(Account accns: acctsContacts){
                
            	integer noOfContacts = accns.Contacts.size();
                System.debug('Number of Contacts' +noOfContacts);
                    
                accns.Number_of_Contacts__c = noOfContacts;                 
                
            	}                        
       
       }        
        
    }

}

@isTest
public class AccountProcessorTest {
    
    @isTest
    public static void testcountContacts(){
        
        //Test Data Preparation - Create new accounts
        ID testAccID;
        List<ID> testAccIdsList = new List<ID>();
        List<Account> testAccount = new List<Account>{
            
            new Account(Name ='TestAccount 1'),
            new Account(Name = 'TestAccount 2'),
            new Account(Name = 'TestAccount 3'),
            new Account(Name = 'TestAccount 4')
        };
            
            insert testAccount;  
        
        //Create 2 contact for each Account
        List<Contact>consList = new List<Contact>();
        for (Account eachAccount:testAccount){
            
            for(integer i=0; i<2; i++){
                
               // List<Contact>consList = new List<Contact>{
                    
                  Contact cons = new Contact(Firstname ='Contact'+i, Lastname = 'Test'+i, AccountId = eachAccount.Id);
                  consList.add(cons);
            }
            
        }
        
        insert conslist;
        
        System.debug('Number of Contacts'+conslist.size());
        
        System.debug('Contacts'+conslist);
        
            //Getting the IDs of the Accounts
            for(Account testaccn:testAccount){
                
                //testAccId = [Select ID from Account 
                             //WHERE Account.ID =:testaccn.Id];
                    
                testAccIdsList.add(testaccn.ID);
                
            }
        
        //Test Starts 
        Test.startTest();
         
        AccountProcessor.countContacts(testAccIdsList);
            
        Test.stopTest();
        
           List<Account>accContactPresent = new list<Account>();
        
           System.debug('List of IDs'+testAccIdsList);
           
           for(Id eachaccID :testAccIdsList){
           
                // This SOQL is not pulling the Number_of_Contacts field
                
                Account contactCount = [Select Match_Billing_Address__c, Number_of_Contacts__c from Account 
                                   		WHERE ID= :eachaccID];
               
           		accContactPresent.add(contactCount);
           
           }  
           for(Account foreachContact :accContactPresent){
               
            	System.debug('Contacts Present'+accContactPresent);
            
            	System.assertEquals(2, foreachContact.Number_of_Contacts__c);
               
         }
        
           
    }

}