old_contents: import Ledger
  from Transaction import Transaction
  
  import unittest
  
  class TestLedger(unittest.TestCase) :
  
      def setUp(self) :
          self.test_object = Ledger.Ledger()
  
      def tearDown(self) :
          pass
  
      def test_not_None(self) :
          self.assertIsNotNone(self.test_object)
  
      def test_add_transaction(self) :
          transaction = Transaction()
          self.test_object.add_transaction(transaction)
          self.assertIn(transaction, self.test_object)
  
new_contents: import Ledger
  from Transaction import Transaction
  
  import unittest
  
  class TestLedger(unittest.TestCase) :
  
      def setUp(self) :
          self.test_object = Ledger.Ledger()
  
      def tearDown(self) :
          pass
  
      def test_not_None(self) :
          self.assertIsNotNone(self.test_object)
  
      def test_add_transaction(self) :
          transaction = Transaction()
          self.test_object.add_transaction(transaction)
          self.assertIn(transaction, self.test_object)
  
      def test_different_transaction_is_not_in_ledger(self) :
          transaction1 = Transaction()
          transaction2 = Transaction()
          self.test_object.add_transaction(transaction1)
          self.assertNotIn(transaction2, self.test_object)
  
subject: Add test to smoke out contains problem in Ledger