old_contents: from django.test import TestCase
new_contents: from django.conf import settings
  from django.core.exceptions import ImproperlyConfigured
  from django.test import TestCase, modify_settings
  
  from boardinghouse.schema import get_schema_model
  
  
  class TestSwappableModel(TestCase):
  
      @modify_settings()
      def test_schema_model_app_not_found(self):
          settings.BOARDINGHOUSE_SCHEMA_MODEL = 'foo.bar'
          with self.assertRaises(ImproperlyConfigured):
              get_schema_model()
  
      @modify_settings()
      def test_schema_model_model_not_found(self):
          settings.BOARDINGHOUSE_SCHEMA_MODEL = 'boardinghouse.NotSchemaModel'
          with self.assertRaises(ImproperlyConfigured):
              get_schema_model()
  
      @modify_settings()
      def test_invalid_schema_model_string(self):
          settings.BOARDINGHOUSE_SCHEMA_MODEL = 'foo__bar'
          with self.assertRaises(ImproperlyConfigured):
              get_schema_model()
  
subject: Write tests for swappable model.