  from django.utils import six
  
  from .models import (
      Book, Car, CustomManager, CustomQuerySet, DeconstructibleCustomManager,
      FunPerson, OneToOneRestrictedModel, Person, PersonFromAbstract,
      PersonManager, PublishedBookManager, RelatedModel, RestrictedModel,
  )
  
  
  class CustomManagerTests(TestCase):
      custom_manager_names = [
 
</s> remove from django.test import TestCase
 </s> add from django.test import TestCase, ignore_warnings </s> remove from django.db.models.manager import ensure_default_manager
 </s> add from django.db.models.manager import Manager </s> remove from django.test import TestCase
 </s> add from django.test import TestCase, ignore_warnings
from django.utils.deprecation import RemovedInDjango20Warning
    FastCarAsBase, FastCarAsDefault, FunPerson, OneToOneRestrictedModel,
    Person, PersonFromAbstract, PersonManager, PublishedBookManager,
    RelatedModel, RestrictedModel,
  from django.utils import six
  
  from .models import (
      Book, Car, CustomManager, CustomQuerySet, DeconstructibleCustomManager,
    FastCarAsBase, FastCarAsDefault, FunPerson, OneToOneRestrictedModel,
    Person, PersonFromAbstract, PersonManager, PublishedBookManager,
    RelatedModel, RestrictedModel,
    FastCarAsBase, FastCarAsDefault, FunPerson, OneToOneRestrictedModel,
    Person, PersonFromAbstract, PersonManager, PublishedBookManager,
    RelatedModel, RestrictedModel,
  )
  
  
  class CustomManagerTests(TestCase):
      custom_manager_names = [
keep keep keep keep replace replace keep keep keep keep keep
 Fixed #10506, #13793, #14891, #25201 -- Introduced new APIs to specify models' default and base managers.

This deprecates use_for_related_fields.

Old API:

class CustomManager(models.Model):
    use_for_related_fields = True

class Model(models.Model):
    custom_manager = CustomManager()

New API:

class Model(models.Model):
    custom_manager = CustomManager()

    class Meta:
        base_manager_name = 'custom_manager'

Refs #20932, #25897.

Thanks Carl Meyer for the guidance throughout this work.
Thanks Tim Graham for writing the docs. 
tests/custom_managers/tests.py