Fix tests for py2/3 compat

tests/test_serializer_bulk_update.py

@@ -3,6 +3,7 @@ Tests to cover bulk create and update using serializers.
 """
 from __future__ import unicode_literals
 from django.test import TestCase
+from django.utils import six
 from rest_framework import serializers
 
 
@@ -82,10 +83,12 @@ class BulkCreateSerializerTests(TestCase):
         serializer = self.BookSerializer(data=data, many=True)
         self.assertEqual(serializer.is_valid(), False)
 
+        text_type_string = six.text_type.__name__
+        message = 'Invalid data. Expected a dictionary, but got %s.' % text_type_string
         expected_errors = [
-            {'non_field_errors': ['Invalid data. Expected a dictionary, but got unicode.']},
-            {'non_field_errors': ['Invalid data. Expected a dictionary, but got unicode.']},
-            {'non_field_errors': ['Invalid data. Expected a dictionary, but got unicode.']}
+            {'non_field_errors': [message]},
+            {'non_field_errors': [message]},
+            {'non_field_errors': [message]}
         ]
 
         self.assertEqual(serializer.errors, expected_errors)