[Tests|Py3] Fix prefetch metdata test

deluge/core/torrentmanager.py

@@ -399,7 +399,7 @@ class TorrentManager(component.Component):
         else:
             self.session.remove_torrent(torrent_handle, 1)
 
-        metadata = ''
+        metadata = b''
         if isinstance(torrent_info, lt.torrent_info):
             log.debug('metadata received')
             metadata = torrent_info.metadata()

deluge/tests/test_core.py

@@ -317,7 +317,7 @@ class CoreTestCase(BaseTestCase):
     def test_prefetch_metadata_existing(self):
         """Check another call with same magnet returns existing deferred."""
         magnet = 'magnet:?xt=urn:btih:ab570cdd5a17ea1b61e970bb72047de141bce173'
-        expected = ('ab570cdd5a17ea1b61e970bb72047de141bce173', '')
+        expected = ('ab570cdd5a17ea1b61e970bb72047de141bce173', b'')
 
         def on_result(result):
             self.assertEqual(result, expected)