Add previous tests and implementation

mopidy/backends/__init__.py

@@ -114,6 +114,9 @@ class BasePlaybackController(object):
     def next(self):
         raise NotImplementedError
 
+    def previous(self):
+        raise NotImplementedError
+
     def pause(self):
         raise NotImplementedError
 

mopidy/backends/gstreamer.py

@@ -96,6 +96,20 @@ class GStreamerPlaybackController(BasePlaybackController):
             next_track = playlist.tracks[self.playlist_position+1]
             self.play(next_track)
 
+    def previous(self):
+        playlist = self.backend.current_playlist.playlist
+
+        if not self.current_track:
+            self.play()
+        elif not playlist.tracks:
+            self.stop()
+        elif self.playlist_position - 1 > 0:
+            first_track = playlist.tracks[0]
+            self.play(first_track)
+        else:
+            previous_track = playlist.tracks[self.playlist_position-1]
+            self.play(previous_track)
+
     @property
     def volume(self):
         return int(self.bin.get_property('volume') * 100)

tests/backends/basetests.py

@@ -290,15 +290,26 @@ class BasePlaybackControllerTest(object):
         self.assertEqual(playback.current_track, tracks[-1])
         self.assertEqual(playback.playlist_position, len(tracks) - 1)
 
-    def test_previous(self):
+    def test_next_for_empty_playlist(self):
         raise NotImplementedError
 
+    @populate_playlist
+    def test_previous(self):
+        tracks = self.backend.current_playlist.playlist.tracks
+        self.playback.play()
+        self.playback.next()
+        self.playback.previous()
+        self.assertEqual(self.playback.current_track, tracks[0])
+
     def test_previous_triggers_playback(self):
         raise NotImplementedError
 
     def test_previous_at_start_of_playlist(self):
         raise NotImplementedError
 
+    def test_previous_for_empty_playlist(self):
+        raise NotImplementedError
+
     @populate_playlist
     def test_next_track_before_play(self):
         tracks = self.backend.current_playlist.playlist.tracks