Corrected deprecation warning silencing of SubfieldBase.

tests/field_subclassing/fields.py

@@ -1,13 +1,23 @@
 from __future__ import unicode_literals
 
 import json
+import warnings
 
 from django.db import models
 from django.utils.encoding import force_text
 from django.utils import six
+from django.utils.deprecation import RemovedInDjango20Warning
 from django.utils.encoding import python_2_unicode_compatible
 
 
+# Catch warning about subfieldbase  -- remove in Django 2.0
+warnings.filterwarnings(
+    'ignore',
+    'SubfieldBase has been deprecated. Use Field.from_db_value instead.',
+    RemovedInDjango20Warning
+)
+
+
 @python_2_unicode_compatible
 class Small(object):
     """