  from django.db.transaction import atomic
  from django.db.utils import IntegrityError, DatabaseError
  from django.utils import six
  
  from .test_base import MigrationTestBase
  
 
</s> remove from django.test import override_settings
from django.db import connection, migrations, models, router
 </s> add from django.db import connection, migrations, models </s> remove from django.db import connections, DEFAULT_DB_ALIAS, router
from django.test import TestCase
 </s> add from django.db import connections, DEFAULT_DB_ALIAS
from django.test import TestCase, override_settings </s> remove from django.db import connections, models, router
from django.test import TestCase
from django.test.utils import captured_stdout, override_settings
 </s> add from django.db import connections, models
from django.test import TestCase, override_settings
from django.test.utils import captured_stdout </s> remove from django.db import connection, router
 </s> add from django.db import connection </s> remove from django.db import connection, connections, router, transaction
 </s> add from django.db import connection, connections, transaction
from django.test import override_settings
  from django.db.transaction import atomic
  from django.db.utils import IntegrityError, DatabaseError
from django.test import override_settings
  from django.utils import six
  
  from .test_base import MigrationTestBase
  
keep add keep keep keep keep
 Replaced router.routers usage with override_settings(DATABASE_ROUTERS); refs #23933. 
tests/migrations/test_operations.py