new_contents: import string
  import langcodes
  
  def test_alpha2_to_alpha3():
      """
      Test that each valid alpha2 code has a corresponding, unique alpha3 code.
      """
      seen = set()
      for letter1 in string.ascii_lowercase:
          for letter2 in string.ascii_lowercase:
              code = letter1 + letter2
              language = langcodes.get(code, normalize=False)
              if language.is_valid():
                  alpha3 = language.to_alpha3()
  
                  # These four 2-letter codes exist only as aliases, and don't have
                  # their own unique 3-letter codes. All other 2-letter codes should
                  # uniquely map to 3-letter codes.
                  if code not in {'in', 'iw', 'ji', 'jw'}:
                      assert alpha3 not in seen
                      seen.add(alpha3)
  
subject: add test for completeness of to_alpha3()