input: Write a python function to create a list of Student objects and return the names of students who have a grade above a specified threshold.
  ```python
  class Student:
      def __init__(self, name, age, grade):
          self.name = name
          self.age = age
          self.grade = grade
  
      def get_name(self):
          return self.name
  
      def get_age(self):
          return self.age
   
      def get_grade(self):
          return self.grade
  
  def get_students_above_grade(students, threshold):
      # Your code here
  
  # Test cases
  students_list = [
      Student("Alice", 20, 85),
      Student("Bob", 21, 75),
      Student("Charlie", 22, 90),
      Student("David", 23, 65)
  ]
  assert get_students_above_grade(students_list, 80) == ["Alice", "Charlie"]
  assert get_students_above_grade(students_list, 70) == ["Alice", "Bob", "Charlie"]
  assert get_students_above_grade(students_list, 60) == ["Alice", "Bob", "Charlie", "David"]
output: def get_students_above_grade(students, threshold):
      return [student.get_name() for student in students if student.get_grade() > threshold]