old_contents: """Unit tests for cat2cohort."""
  
  import unittest
  from cat2cohort import api_url
  
  
  class TestCat2Cohort(unittest.TestCase):
  
      """Test methods from Cat2Cohort."""
  
      pass
  
new_contents: """Unit tests for cat2cohort."""
  
  import unittest
  from cat2cohort import api_url
  
  
  class TestCat2Cohort(unittest.TestCase):
  
      """Test methods from Cat2Cohort."""
  
      def test_api_url(self):
          """Test api_url."""
          values = [
              ('fr', 'https://fr.wikipedia.org/w/api.php'),
              ('en', 'https://en.wikipedia.org/w/api.php'),
          ]
          for value, expected in values:
              self.assertEqual(api_url(value), expected)
  
subject: Add untittest for api_url