//will do an action on all of the customers
 public void DoToAllCustomers(CustomerAction action)
 {
     foreach (Customer customer in _customers)
     {
         action.Invoke(customer);
         if (customer.Balance >= 1000000)
         {
             UnreasonableCustomerBalanceEventArgs args = new UnreasonableCustomerBalanceEventArgs(customer.Balance);
             OnUnreasonableCustomerBalance?.Invoke(customer, args);
         }
     }
 }