  from __future__ import unicode_literals
  from django.utils.datastructures import MultiValueDict
  from django.test import TestCase
  from rest_framework import serializers
  from rest_framework.tests.models import (HasPositiveIntegerAsChoice, Album, ActionItem, Anchor, BasicModel,
      BlankFieldModel, BlogPost, BlogPostComment, Book, CallableDefaultValueModel, DefaultValueModel,
 
</s> remove     ManyToManyModel, Person, ReadOnlyManyToManyModel, Photo)
 </s> add     ManyToManyModel, Person, ReadOnlyManyToManyModel, Photo, SeveralChoicesModel) </s> remove         self.assertEqual(s.errors,  {'decimal_field': ['Ensure that there are no more than 4 digits in total.']}) </s> add 
from django.db.models.fields import BLANK_CHOICE_DASH
  from __future__ import unicode_literals
from django.db.models.fields import BLANK_CHOICE_DASH
  from django.utils.datastructures import MultiValueDict
  from django.test import TestCase
  from rest_framework import serializers
  from rest_framework.tests.models import (HasPositiveIntegerAsChoice, Album, ActionItem, Anchor, BasicModel,
      BlankFieldModel, BlogPost, BlogPostComment, Book, CallableDefaultValueModel, DefaultValueModel,
add keep keep keep keep keep
 Adding `BLANK_CHOICE_DASH` as a choice if the model's field isn't required 
rest_framework/tests/serializer.py