  from django.db.models import Prefetch, QuerySet
  from django.db.models.query import get_prefetcher
  from django.test import TestCase, override_settings
  from django.test.utils import CaptureQueriesContext
  from django.utils import six
  from django.utils.encoding import force_text
  
  from .models import (
      Author, Author2, AuthorAddress, AuthorWithAge, Bio, Book, Bookmark,
      BookReview, BookWithYear, Comment, Department, Employee, FavoriteAuthors,
 
</s> remove from django.utils import six
 </s> add  </s> remove from django.utils import six
 </s> add  </s> remove from django.utils import six
 </s> add  </s> remove from django.utils import six
 </s> add  </s> remove from django.utils import six
 </s> add 
  from django.db.models import Prefetch, QuerySet
  from django.db.models.query import get_prefetcher
  from django.test import TestCase, override_settings
  from django.test.utils import CaptureQueriesContext

  from django.utils.encoding import force_text
  
  from .models import (
      Author, Author2, AuthorAddress, AuthorWithAge, Bio, Book, Bookmark,
      BookReview, BookWithYear, Comment, Department, Employee, FavoriteAuthors,
keep keep keep keep replace keep keep keep keep keep
 Refs #23919 -- Removed six.<various>_types usage

Thanks Tim Graham and Simon Charette for the reviews. 
tests/prefetch_related/tests.py