When an account's phone number is updated, all related contact's 'Other Phone' must be updated. Do not update the contact's phone if the contact's country differs from the account's country

UpdateContactPhoneTrigger

/*
 When an account's phone number is updated, all related contact's  'Other Phone' must be updated
 Do not update the contact's phone if the contact's country differs from the account's country
 */ 

trigger UpdateContactPhone on Account (before update) {
	
    for(Account acc : Trigger.new){
        //Make sure the phone number is populated
        if(acc.Phone != null){
            
            //Find relevant contacts
            List<Contact> contacts = [SELECT Id, MailingCountry
                                        FROM Contact
                                       WHERE AccountId = :acc.Id];
            
            //Loop thru and update each contact
            for(Contact con : contacts){
                if(con.MailingCountry != null && con.MailingCountry == acc.BillingCountry) {
                	con.OtherPhone = acc.Phone;
                }    
            }
            update contacts;
        }
    }
}


//Test Class

@isTest
private class UpdateContactPhoneTest {
	
    @isTest static void updatePhoneOnAccount(){
        String country = 'US';
        Account acc = new Account();
        acc.Name = 'Windsor Hotels';
        acc.BillingCountry = country;
        insert acc;
        
      	List<Contact> contacts = new List<Contact>();
        for(Integer i = 0; i < 5; i++){
            String iString = String.valueOf(i);
            Contact myCon = new Contact();
            myCon.FirstName = 'Z'+iString;
            myCon.LastName = 'Z'+iString;
            myCon.AccountId = acc.Id;
            myCon.MailingCountry = country;
            contacts.add(myCon);
        }
        //Create a contact of a diff country
        Contact diffCon = new Contact();
            diffCon.FirstName = 'Alisha';
            diffCon.LastName = 'Matts';
            diffCon.AccountId = acc.Id;
            diffCon.MailingCountry = country+'A';
        contacts.add(diffCon);
        
        insert contacts;
        
        String phoneNumber = '4350987878';
        acc.Phone = phoneNumber;
        update acc;
        
        contacts = [SELECT OtherPhone
                      FROM Contact
                     WHERE AccountId = :acc.Id
                   ORDER BY FirstName ASC];
        
        //Assert in loops
       // for(Contact con : contacts){
         //   System.assertEquals(phoneNumber, con.OtherPhone);
        //}
        
        System.assertEquals(phoneNumber, contacts.get(1).OtherPhone);
        System.assertEquals(null, contacts.get(0).OtherPhone);
    }
}