  class RegexValidationTest(TestCase):
      def test_create_failed(self):
          serializer = BookSerializer(data={'isbn': '1234567890'})
          self.assertFalse(serializer.is_valid())
          self.assertEquals(serializer.errors, {'isbn': [u'isbn has to be exact 13 numbers']})
  
          serializer = BookSerializer(data={'isbn': '12345678901234'})
          self.assertFalse(serializer.is_valid())
          self.assertEquals(serializer.errors, {'isbn': [u'isbn has to be exact 13 numbers']})
  
 
</s> remove         self.assertEquals(serializer.errors, {'isbn': [u'isbn has to be exact 13 numbers']})
 </s> add         self.assertEquals(serializer.errors, {'isbn': ['isbn has to be exact 13 numbers']}) </s> remove         self.assertEquals(serializer.errors, {'isbn': [u'isbn has to be exact 13 numbers']})
 </s> add         self.assertEquals(serializer.errors, {'isbn': ['isbn has to be exact 13 numbers']}) </s> remove         self.assertEquals(serializer.errors, {'info': [u'Ensure this value has at most 12 characters (it has 13).']})
 </s> add         self.assertEquals(serializer.errors, {'info': ['Ensure this value has at most 12 characters (it has 13).']}) </s> remove         self.assertEquals(serializer.errors, {'content': [u'Test not in value']})
 </s> add         self.assertEquals(serializer.errors, {'content': ['Test not in value']}) </s> remove         self.assertEquals(serializer.errors, {'content': [u'Ensure this value has at most 1000 characters (it has 1001).']})
 </s> add         self.assertEquals(serializer.errors, {'content': ['Ensure this value has at most 1000 characters (it has 1001).']})
        self.assertEquals(serializer.errors, {'isbn': ['isbn has to be exact 13 numbers']})
  class RegexValidationTest(TestCase):
      def test_create_failed(self):
          serializer = BookSerializer(data={'isbn': '1234567890'})
          self.assertFalse(serializer.is_valid())
        self.assertEquals(serializer.errors, {'isbn': ['isbn has to be exact 13 numbers']})
  
          serializer = BookSerializer(data={'isbn': '12345678901234'})
          self.assertFalse(serializer.is_valid())
          self.assertEquals(serializer.errors, {'isbn': [u'isbn has to be exact 13 numbers']})
  
keep keep keep keep replace keep keep keep keep keep
 First passing test under p3k \o/ 
rest_framework/tests/serializer.py