Fix song counter and inconsistent queue state

tests/test_music_player.py

@@ -25,15 +25,36 @@ class MusicPlayerQueueTest(unittest.IsolatedAsyncioTestCase):
         self.assertIs(voice_client.playing, track)
         self.assertEqual(player.state(GUILD).index, 0)
 
-    async def test_single_play_budget_drops_track_from_queue(self):
+    async def test_last_play_remains_pointed_to_until_playback_finishes(self):
         player, _ = build_player(default_plays=1)
         track = FakeTrack("a")
         await player.enqueue(GUILD, track)
 
         state = player.state(GUILD)
+        self.assertEqual(state.queue, [track])
+        self.assertEqual(state.index, 0)
+        self.assertIs(state.current, track)
+
+        await player.play_next(GUILD, advance=True)
+
         self.assertEqual(state.queue, [])
         self.assertEqual(state.index, -1)
-        self.assertIs(state.current, track)
+        self.assertIsNone(state.current)
+
+    async def test_last_play_of_recreated_track_is_removed_after_callback(self):
+        player, _, state = await self._queue_abc(default_plays=2)
+        state.loop_mode = LoopMode.TRACK
+
+        await player.play_next(GUILD, advance=True)
+        self.assertEqual([track.id for track in state.queue], ["a", "b", "c"])
+        self.assertEqual(state.index, 0)
+        self.assertEqual(state.current.plays_left, 0)
+
+        await player.play_next(GUILD, advance=True)
+
+        self.assertEqual([track.id for track in state.queue], ["b", "c"])
+        self.assertEqual(state.index, 0)
+        self.assertEqual(state.current.id, "b")
 
     async def test_enqueue_while_playing_only_appends(self):
         _, _, state = await self._queue_abc()