Fix #1218

Output a track's Last-Modified stamp in ISO 8601 format, as MPD does.

Output nothing if track has no last-modified stamp.

The test has to use datetime to work out what the output will look like,
because it is local-time zone dependant.

mopidy/mpd/translator.py

@@ -89,7 +89,7 @@ def track_to_mpd_format(track, position=None, stream_title=None):
 
     if track.last_modified is not None:
         datestring = datetime.datetime.fromtimestamp(
-            track.last_modified // 1000).strftime('%Y-%m-%dT%H:%M:%S%Z')
+            track.last_modified // 1000).isoformat()
         result.append(('Last-Modified', datestring))
 
     if track.musicbrainz_id is not None:

tests/mpd/test_translator.py

@@ -1,5 +1,6 @@
 from __future__ import absolute_import, unicode_literals
 
+import datetime
 import unittest
 
 from mopidy.internal import path
@@ -81,6 +82,12 @@ class TrackMpdFormatTest(unittest.TestCase):
 
     def test_track_to_mpd_format_with_last_modified(self):
         track = self.track.replace(last_modified=995303899000)
+        # Due to this being local time-zone dependant, we have
+        # to calculate what the Last-Modified output will look like
+        # on the machine where the tests are being run. So this only tests
+        # that the output is actually there.
+        datestring = datetime.datetime.fromtimestamp(
+            track.last_modified // 1000).isoformat()
         result = translator.track_to_mpd_format(track)
         self.assertIn(('file', 'a uri'), result)
         self.assertIn(('Time', 137), result)
@@ -94,7 +101,7 @@ class TrackMpdFormatTest(unittest.TestCase):
         self.assertIn(('Track', '7/13'), result)
         self.assertIn(('Date', '1977-01-01'), result)
         self.assertIn(('Disc', 1), result)
-        self.assertIn(('Last-Modified', '2001-07-16T18:18:19'), result)
+        self.assertIn(('Last-Modified', datestring), result)
         self.assertNotIn(('Comment', 'a comment'), result)
         self.assertEqual(len(result), 13)