text: import unittest
  from reverse_string import reverse
  
  class TestReverseString(unittest.TestCase):
    def test_empty_string(self):
      self.assertEqual(reverse(''), '')
  
    def test_none(self):
      self.assertEqual(reverse(None), None)
  
    def test_single_char(self):
      self.assertEqual(reverse('a'), 'a')
  
    def test_small_string(self):
      self.assertEqual(reverse('abc'), 'cba')
  
    def test_larger_string(self):
      self.assertEqual(reverse('A man, a plan, a canal: Panama'), 'amanaP :lanac a ,nalp a ,nam A')
  
  if __name__ == '__main__':
    unittest.main()