new_contents: import unittest
  
  from aids.stack.queue_two_stacks import QueueUsingTwoStacks
  
  class QueueTwoStacksTestCase(unittest.TestCase):
      '''
      Unit tests for the Queue data structure implemented using two stacks
  
      '''
   
      def setUp(self):
  		self.test_queue = QueueUsingTwoStacks()
  
      def test_queue_initialization(self):
  		self.assertTrue(isinstance(self.test_queue, QueueUsingTwoStacks))
  
      def test_queue_is_empty(self):
          self.assertTrue(self.test_queue.is_empty())
  
      def test_queue_enqueue(self):
  		self.test_queue.enqueue(1)
  		self.assertEqual(len(self.test_queue), 1)
  		
  	def test_queue_dequeue(self):
  		self.test_queue.enqueue(1)
  		self.assertEqual(self.test_queue.dequeue(), 1)
  		
  	def test_queue_len(self):
  		self.test_queue.enqueue(1)
  		self.assertEqual(len(self.test_queue), 1)
  
      def tearDown(self):
          pass
  
subject: Add unit tests for queue_two_stacks