input: Write a python function to create an Employee object, change its age, and verify its attributes using assert statements.
  assert emp.get_name() == "John"
  assert emp.get_age() == 25
  emp.set_age(30)
  assert emp.get_age() == 30
output: class Employee:
      def __init__(self, name, age):
          self._name = name
          self._age = age
  
      def get_name(self):
          return self._name
  
      def get_age(self):
          return self._age
  
      def set_age(self, age):
          self._age = age
  
  # Creating an Employee object
  emp = Employee("John", 25)
  # Verifying the attributes
  assert emp.get_name() == "John"
  assert emp.get_age() == 25
  # Changing the age
  emp.set_age(30)
  # Verifying the changed age
  assert emp.get_age() == 30