old_contents: import unittest
  from number_to_words import NumberToWords
  
  
  class TestNumberToWords(unittest.TestCase):
      def setUp(self):
          self.n2w = NumberToWords()
  
      def tearDown(self):
          self.n2w = None
  
  if __name__ == '__main__':
      unittest.main()
  
new_contents: import unittest
  from number_to_words import NumberToWords
  
  
  class TestNumberToWords(unittest.TestCase):
      def setUp(self):
          self.n2w = NumberToWords()
  
      def tearDown(self):
          self.n2w = None
  
      def test_zero_and_single_digits(self):
          NUMBERS = {
              0: 'zero', 1: 'one', 2: 'two', 3: 'three', 4: 'four', 5: 'five',
              6: 'six', 7: 'seven', 8: 'eight', 9: 'nine'
          }
          self.assert_numbers_equal_to_strings(NUMBERS)
  
      def assert_numbers_equal_to_strings(self, numbers):
          for number, string in numbers.iteritems():
              self.assertEqual(string, self.n2w.convert(number))
  
  if __name__ == '__main__':
      unittest.main()
  
subject: Add tests for number 0 to 9