new_contents: import os
  import unittest
  
  from yithlibraryserver.config import read_setting_from_env
  
  
  class ConfigTests(unittest.TestCase):
  
      def test_read_setting_from_env(self):
          settings = {
              'foo_bar': '1',
              }
  
          self.assertEqual('1', read_setting_from_env(settings, 'foo_bar'))
  
          self.assertEqual('default',
                           read_setting_from_env(settings, 'new_option', 'default'))
          self.assertEqual(None,
                           read_setting_from_env(settings, 'new_option'))
  
          os.environ['FOO_BAR'] = '2'
          self.assertEqual('2', read_setting_from_env(settings, 'foo_bar'))
  
subject: Add a test for the read_setting_from_env function