input: Write a python function to create and test a CustomerHistory class that tracks purchases.
  assert cust1.get_purchase_history() == [], 'Initial history should be empty'
  cust1.add_purchase('apple')
  assert cust1.get_purchase_history() == ['apple'], 'History should contain one purchase'
  cust1.add_purchase('banana')
  assert cust1.get_purchase_history() == ['apple', 'banana'], 'History should contain two purchases'
  cust2 = CustomerHistory(2)
  assert cust2.get_purchase_history() == [], 'Initial history for a new customer should be empty'
output: class CustomerHistory:
      def __init__(self, customer_id):
          self.customer_id = customer_id
          self.purchase_history = []
  
      def add_purchase(self, item):
          self.purchase_history.append(item)
  
      def get_purchase_history(self):
          return self.purchase_history
  
  # Test the CustomerHistory class
  cust1 = CustomerHistory(1)
  assert cust1.get_purchase_history() == [], 'Initial history should be empty'
  cust1.add_purchase('apple')
  assert cust1.get_purchase_history() == ['apple'], 'History should contain one purchase'
  cust1.add_purchase('banana')
  assert cust1.get_purchase_history() == ['apple', 'banana'], 'History should contain two purchases'
  cust2 = CustomerHistory(2)
  assert cust2.get_purchase_history() == [], 'Initial history for a new customer should be empty'