old_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)
  
      def test_negative_price_exception(self):
          """An update with a negative price should return a value error.
  
          """
          stock = Stock("GOOG")
          try:
              stock.update(datetime(2014, 2, 12), price=-10)
          except ValueError:
              return
          self.fail("ValueError was not raised")
  
  
  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)
  
      def test_negative_price_exception(self):
          """An update with a negative price should return a value error.
  
          """
          stock = Stock("GOOG")
          self.assertRaises(ValueError, stock.update, datetime(2014, 2, 13), -10)
  
  
  if __name__ == "__main__":
      unittest.main()
  
subject: Update negative price exception test to use assertRaises.