diff --git a/swh/core/tests/test_serializers.py b/swh/core/tests/test_serializers.py
index 490dff0..49e5927 100644
--- a/swh/core/tests/test_serializers.py
+++ b/swh/core/tests/test_serializers.py
@@ -1,75 +1,75 @@
 # Copyright (C) 2015  The Software Heritage developers
 # See the AUTHORS file at the top-level directory of this distribution
 # License: GNU General Public License version 3, or any later version
 # See top-level LICENSE file for more information
 
 import datetime
 import json
 import unittest
 from uuid import UUID
 
 from nose.tools import istest
 
 from swh.core.serializers import SWHJSONDecoder, SWHJSONEncoder
 from swh.core.serializers import msgpack_dumps, msgpack_loads
 
 
 class Serializers(unittest.TestCase):
     def setUp(self):
         self.tz = datetime.timezone(datetime.timedelta(minutes=118))
 
         self.data = {
-            "bytes": b"123456789\x99\xaf\xff\x00\x12",
-            "datetime_naive": datetime.datetime(2015, 1, 1, 12, 4, 42, 231455),
-            "datetime_tz": datetime.datetime(2015, 3, 4, 18, 25, 13, 1234,
+            'bytes': b'123456789\x99\xaf\xff\x00\x12',
+            'datetime_naive': datetime.datetime(2015, 1, 1, 12, 4, 42, 231455),
+            'datetime_tz': datetime.datetime(2015, 3, 4, 18, 25, 13, 1234,
                                              tzinfo=self.tz),
-            "datetime_utc": datetime.datetime(2015, 3, 4, 18, 25, 13, 1234,
+            'datetime_utc': datetime.datetime(2015, 3, 4, 18, 25, 13, 1234,
                                               tzinfo=datetime.timezone.utc),
-            "swhtype": "fake",
-            "swh_dict": {"swhtype": 42, "d": "test"},
-            "random_dict": {"swhtype": 43},
-            "uuid": UUID('cdd8f804-9db6-40c3-93ab-5955d3836234'),
+            'swhtype': 'fake',
+            'swh_dict': {'swhtype': 42, 'd': 'test'},
+            'random_dict': {'swhtype': 43},
+            'uuid': UUID('cdd8f804-9db6-40c3-93ab-5955d3836234'),
         }
 
         self.encoded_data = {
-            "bytes": {"swhtype": "bytes", "d": "F)}kWH8wXmIhn8j01^"},
-            "datetime_naive": {"swhtype": "datetime",
-                               "d": "2015-01-01T12:04:42.231455"},
-            "datetime_tz": {"swhtype": "datetime",
-                            "d": "2015-03-04T18:25:13.001234+01:58"},
-            "datetime_utc": {"swhtype": "datetime",
-                             "d": "2015-03-04T18:25:13.001234+00:00"},
-            "swhtype": "fake",
-            "swh_dict": {"swhtype": 42, "d": "test"},
-            "random_dict": {"swhtype": 43},
-            "uuid": {"swhtype": "uuid",
-                     "d": "cdd8f804-9db6-40c3-93ab-5955d3836234"},
+            'bytes': {'swhtype': 'bytes', 'd': 'F)}kWH8wXmIhn8j01^'},
+            'datetime_naive': {'swhtype': 'datetime',
+                               'd': '2015-01-01T12:04:42.231455'},
+            'datetime_tz': {'swhtype': 'datetime',
+                            'd': '2015-03-04T18:25:13.001234+01:58'},
+            'datetime_utc': {'swhtype': 'datetime',
+                             'd': '2015-03-04T18:25:13.001234+00:00'},
+            'swhtype': 'fake',
+            'swh_dict': {'swhtype': 42, 'd': 'test'},
+            'random_dict': {'swhtype': 43},
+            'uuid': {'swhtype': 'uuid',
+                     'd': 'cdd8f804-9db6-40c3-93ab-5955d3836234'},
         }
 
         self.generator = (i for i in range(5))
         self.gen_lst = list(range(5))
 
     @istest
     def round_trip_json(self):
         data = json.dumps(self.data, cls=SWHJSONEncoder)
         self.assertEqual(self.data, json.loads(data, cls=SWHJSONDecoder))
 
     @istest
     def encode_swh_json(self):
         data = json.dumps(self.data, cls=SWHJSONEncoder)
         self.assertEqual(self.encoded_data, json.loads(data))
 
     @istest
     def round_trip_msgpack(self):
         data = msgpack_dumps(self.data)
         self.assertEqual(self.data, msgpack_loads(data))
 
     @istest
     def generator_json(self):
         data = json.dumps(self.generator, cls=SWHJSONEncoder)
         self.assertEqual(self.gen_lst, json.loads(data, cls=SWHJSONDecoder))
 
     @istest
     def generator_msgpack(self):
         data = msgpack_dumps(self.generator)
         self.assertEqual(self.gen_lst, msgpack_loads(data))