Add mechanism for tearing down backend cleanly

mopidy/backends/__init__.py

@@ -14,6 +14,9 @@ class BaseBackend(object):
     stored_playlists = None
     uri_handlers = []
 
+    def destroy(self):
+        self.playback.destroy()
+
 class BaseCurrentPlaylistController(object):
     def __init__(self, backend):
         self.backend = backend
@@ -164,3 +167,6 @@ class BasePlaybackController(object):
     @property
     def volume(self):
         return self._volume
+
+    def destroy(self):
+        pass

mopidy/backends/gstreamer.py

@@ -93,3 +93,7 @@ class GStreamerPlaybackController(BasePlaybackController):
     @volume.setter
     def volume(self, value):
         return self.bin.set_property('volume', float(value) / 100)
+
+    def destroy(self):
+        self.bin.set_state(gst.STATE_NULL)
+        del self.bin

tests/backends/basetests.py

@@ -196,6 +196,9 @@ class BasePlaybackControllerTest(object):
         self.backend = self.backend_class()
         self.playback = self.backend.playback
 
+    def tearDown(self):
+        self.backend.destroy()
+
     def test_initial_state_is_stopped(self):
         self.assertEqual(self.playback.state, self.playback.STOPPED)