Handle shuffeling of subset

mopidy/backends/__init__.py

@@ -51,9 +51,14 @@ class BaseCurrentPlaylistController(object):
 
     def shuffle(self, start=None, end=None):
         tracks = self.playlist.tracks
-        random.shuffle(tracks)
 
-        self.playlist = Playlist(tracks=tracks)
+        before = tracks[:start or 0]
+        shuffled = tracks[start:end]
+        after = tracks[end or len(tracks):]
+
+        random.shuffle(shuffled)
+
+        self.playlist = Playlist(tracks=before+shuffled+after)
 
 class BasePlaybackController(object):
     PAUSED = 'paused'

tests/backends/__init__.py

@@ -99,6 +99,18 @@ class BaseCurrentPlaylistControllerTest(object):
         self.assertNotEqual(tracks, shuffled_tracks)
         self.assertEqual(set(tracks), set(shuffled_tracks))
 
+    @populate_playlist
+    def test_shuffle_subset(self):
+        tracks = self.controller.playlist.tracks
+        random.seed(1)
+        self.controller.shuffle(1, 3)
+
+        shuffled_tracks = self.controller.playlist.tracks
+
+        self.assertNotEqual(tracks, shuffled_tracks)
+        self.assertEqual(tracks[0], shuffled_tracks[0])
+        self.assertEqual(set(tracks), set(shuffled_tracks))
+
 class BasePlaybackControllerTest(object):
     uris = []
     backend_class = None