[Tests] Make file priority test more consistent.

Our file priority test was using time.sleep to wait until libtorrent
had processed the command. This was sometimes not long enough and the
test would fail. On libtorrent 2.0.3+ there is an alert when the
process has finished, switch to waiting for that in this test to make
the test more consistent. On older libtorrent, make the delay a bit
longer, to try to make the test more consistent there as well.

Closes: https://github.com/deluge-torrent/deluge/pull/373

deluge/tests/test_torrent.py

@@ -10,6 +10,7 @@ from base64 import b64encode
 from unittest import mock
 
 import pytest
+import pytest_twisted
 from twisted.internet import defer, reactor
 from twisted.internet.task import deferLater
 
@@ -80,7 +81,19 @@ class TestTorrent(BaseTestCase):
         }
         return atp
 
-    def test_set_file_priorities(self):
+    @pytest_twisted.ensureDeferred
+    async def test_set_file_priorities(self):
+        if getattr(lt, 'file_prio_alert', None):
+            # Libtorrent 2.0.3 and later has a file_prio_alert
+            prios_set = defer.Deferred()
+            prios_set.addTimeout(1.5, reactor)
+            component.get('AlertManager').register_handler(
+                'file_prio_alert', lambda a: prios_set.callback(True)
+            )
+        else:
+            # On older libtorrent, we just wait a while
+            prios_set = deferLater(reactor, 0.8)
+
         atp = self.get_torrent_atp('dir_with_6_files.torrent')
         handle = self.session.add_torrent(atp)
         torrent = Torrent(handle, {})
@@ -95,7 +108,7 @@ class TestTorrent(BaseTestCase):
         # Test with handle.piece_priorities as handle.file_priorities async
         # updates and will return old value. Also need to remove a priority
         # value as one file is much smaller than piece size so doesn't show.
-        time.sleep(0.6)  # Delay to wait for alert from lt
+        await prios_set  # Delay to wait for alert from lt
         piece_prio = handle.piece_priorities()
         result = all(p in piece_prio for p in [3, 2, 0, 5, 6, 7])
         assert result