diff --git a/test_objstorage.py b/test_objstorage.py
index 7170a54..a242c2d 100644
--- a/test_objstorage.py
+++ b/test_objstorage.py
@@ -1,131 +1,131 @@
 # 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 gzip
 import os
 import shutil
 import tempfile
 import unittest
 
 from io import BytesIO
 from nose.tools import istest
 
 from swh.storage import objstorage
 
 
 class TestObjStorage(unittest.TestCase):
 
     def setUp(self):
         self.content = b'42\n'
 
         self.obj_id = '34973274ccef6ab4dfaaf86599792fa9c3fe4689'  # sha1
         # self.obj_id = 'd81cc0710eb6cf9efd5b920a8453e1e07157b6cd'  # sha1_git
         self.obj_steps = [self.obj_id[0:2], self.obj_id[2:4], self.obj_id[4:6]]
         self.obj_relpath = os.path.join(*(self.obj_steps + [self.obj_id]))
 
         self.tmpdir = tempfile.mkdtemp()
         self.obj_path = os.path.join(self.tmpdir, self.obj_relpath)
 
         self.storage = objstorage.ObjStorage(root=self.tmpdir, depth=3)
 
         self.missing_obj_id = 'f1d2d2f924e986ac86fdf7b36c94bcdf32beec15'
 
     def tearDown(self):
         shutil.rmtree(self.tmpdir)
 
     def assertGzipContains(self, gzip_path, content):
         self.assertEqual(gzip.open(gzip_path, 'rb').read(), content)
 
     @istest
     def add_bytes_w_id(self):
         r = self.storage.add_bytes(self.content, obj_id=self.obj_id)
         self.assertEqual(r, self.obj_id)
         self.assertGzipContains(self.obj_path, self.content)
 
     @istest
     def add_bytes_wo_id(self):
         r = self.storage.add_bytes(self.content)
         self.assertEqual(r, self.obj_id)
         self.assertGzipContains(self.obj_path, self.content)
 
     @istest
     def add_file_w_id(self):
         r = self.storage.add_file(BytesIO(self.content),
                                   len(self.content),
                                   obj_id=self.obj_id)
         self.assertEqual(r, self.obj_id)
         self.assertGzipContains(self.obj_path, self.content)
 
     @istest
     def add_file_wo_id(self):
         r = self.storage.add_file(BytesIO(self.content), len(self.content))
         self.assertEqual(r, self.obj_id)
         self.assertGzipContains(self.obj_path, self.content)
 
     @istest
     def contains(self):
         self.storage.add_bytes(self.content, obj_id=self.obj_id)
-        self.assertTrue(self.obj_id in self.storage)
-        self.assertFalse(self.missing_obj_id in self.storage)
+        self.assertIn(self.obj_id, self.storage)
+        self.assertNotIn(self.missing_obj_id, self.storage)
 
     @istest
     def check_ok(self):
         self.storage.add_bytes(self.content, obj_id=self.obj_id)
         try:
             self.storage.check(self.obj_id)
         except:
             self.fail('integrity check failed')
 
     @istest
     def check_missing(self):
         with self.assertRaises(objstorage.Error):
             self.storage.check(self.obj_id)
 
     @istest
     def check_not_gzip(self):
         self.storage.add_bytes(self.content, obj_id=self.obj_id)
         with open(self.obj_path, 'ab') as f:  # add trailing garbage
             f.write(b'garbage')
         with self.assertRaises(objstorage.Error):
             self.storage.check(self.obj_id)
 
     @istest
     def check_id_mismatch(self):
         self.storage.add_bytes(self.content, obj_id=self.obj_id)
         with gzip.open(self.obj_path, 'wb') as f:  # replace gzipped content
             f.write(b'unexpected content')
         with self.assertRaises(objstorage.Error):
             self.storage.check(self.obj_id)
 
     @istest
     def get_bytes(self):
         self.storage.add_bytes(self.content, obj_id=self.obj_id)
         self.assertEqual(self.storage.get_bytes(self.obj_id),
                          self.content)
 
     @istest
     def get_file_path(self):
         self.storage.add_bytes(self.content, obj_id=self.obj_id)
         path = self.storage._get_file_path(self.obj_id)
         self.assertEqual(os.path.basename(path), self.obj_id)
         self.assertEqual(gzip.open(path, 'rb').read(), self.content)
 
     @istest
     def get_missing(self):
         with self.assertRaises(objstorage.Error):
             with self.storage.get_file_obj(self.missing_obj_id) as f:
                 f.read()
 
     @istest
     def iter(self):
         self.assertEqual(list(iter(self.storage)), [])
         self.storage.add_bytes(self.content, obj_id=self.obj_id)
         self.assertEqual(list(iter(self.storage)), [self.obj_id])
 
     @istest
     def len(self):
         self.assertEqual(len(self.storage), 0)
         self.storage.add_bytes(self.content, obj_id=self.obj_id)
         self.assertEqual(len(self.storage), 1)