[Tests] Fix save_resume_data errors in test_torrent

Error in test_rename_unicode:

   TypeError: object MagicMock can't be used in 'await' expression

Fixed by using AsyncMock that can be awaited.
Added backport asyncmock for Python 3.7

deluge/tests/test_torrent.py

@@ -25,6 +25,11 @@ from deluge.core.rpcserver import RPCServer
 from deluge.core.torrent import Torrent
 from deluge.core.torrentmanager import TorrentManager, TorrentState
 
+try:
+    from unittest.mock import AsyncMock
+except ImportError:
+    from mock import AsyncMock
+
 
 class TestTorrent(BaseTestCase):
     def setup_config(self):
@@ -340,7 +345,7 @@ class TestTorrent(BaseTestCase):
         handle = self.session.add_torrent(atp)
         self.torrent = Torrent(handle, {})
         # Ignore TorrentManager method call
-        TorrentManager.save_resume_data = mock.MagicMock
+        TorrentManager.save_resume_data = AsyncMock()
 
         result = self.torrent.rename_folder('unicode_filenames', 'Горбачёв')
         assert isinstance(result, defer.DeferredList)

requirements-tests.txt

@@ -9,3 +9,4 @@ flake8-isort
 pep8-naming
 mccabe
 pylint
+asyncmock; python_version <= '3.7'