input: Write a python function to create a collection of data points, add new data points to it, and retrieve the list of data points.
  assert dp_collection.get_data_points() == []
  
  dp_collection = DataPointCollection()
  dp_collection.add_data_point(10)
  dp_collection.add_data_point(20)
  assert dp_collection.get_data_points() == [10, 20]
  
  dp_collection.add_data_point(30)
  assert dp_collection.get_data_points() == [10, 20, 30]
output: class DataPointCollection:
      def __init__(self):
          self.data_points = []
  
      def add_data_point(self, point):
          self.data_points.append(point)
  
      def get_data_points(self):
          return self.data_points