old_contents: import unittest
  from datetime import datetime
  
  from stock import Stock
  
  
  class StockTest(unittest.TestCase):
      def test_price_of_a_new_stock_class_should_be_None(self):
          stock = Stock("GOOG")
          self.assertIsNone(stock.price)
  
      def test_stock_update(self):
          """An update should set the price on the stock object.
  
          Notes:
              We will be using the `datetime` module for the timestamp.
          """
          goog = Stock("GOOG")
          goog.update(datetime(2014, 2, 12), price=10)
          self.assertEqual(10, goog.price)
  
  if __name__ == "__main__":
      unittest.main()
  
new_contents: import unittest
  from datetime import datetime
  
  from stock import Stock
  
  
  class StockTest(unittest.TestCase):
      def test_new_stock_price(self):
          """A new stock should have a price that is None.
          """
          stock = Stock("GOOG")
          self.assertIsNone(stock.price)
  
      def test_stock_update(self):
          """An update should set the price on the stock object.
  
          Notes:
              We will be using the `datetime` module for the timestamp.
          """
          stock = Stock("GOOG")
          stock.update(datetime(2014, 2, 12), price=10)
          self.assertEqual(10, stock.price)
  
  if __name__ == "__main__":
      unittest.main()
  
subject: Add comment and clean up code.