input: Write a python function to create a BankAccountHolder instance and test its methods.
  assert account.get_name() == "John Doe"
  assert account.get_card_number() == "1234-5678-9101-1121"
  assert account.get_pin() == "4321"
  assert account.get_balance() == 1000
  account.set_balance(1500)
  assert account.get_balance() == 1500
output: class BankAccountHolder:
      def __init__(self, name, card_number, pin, balance):
          self._name = name
          self._card_number = card_number
          self._pin = pin
          self._balance = balance
  
      def get_name(self):
          return self._name
  
      def get_card_number(self):
          return self._card_number
  
      def get_pin(self):
          return self._pin
  
      def get_balance(self):
          return self._balance
  
      def set_balance(self, new_balance):
          self._balance = new_balance
  
  # Creating an instance of BankAccountHolder
  account = BankAccountHolder("John Doe", "1234-5678-9101-1121", "4321", 1000)
  
  # Testing the methods
  assert account.get_name() == "John Doe"
  assert account.get_card_number() == "1234-5678-9101-1121"
  assert account.get_pin() == "4321"
  assert account.get_balance() == 1000
  account.set_balance(1500)
  assert account.get_balance() == 1500