app: Fix bug when a tag that has no playlist is encountered

software/src/app.py

@@ -69,7 +69,7 @@ class PlayerApp:
 
     def _set_playlist(self, tag: bytes):
         self.playlist = self.playlist_db.getPlaylistForTag(tag)
-        self._play(self.playlist.getCurrentPath())
+        self._play(self.playlist.getCurrentPath() if self.playlist is not None else None)
 
     def _play_next(self):
         if self.playlist is None:

software/tests/test_playerapp.py

@@ -137,3 +137,21 @@ def test_playlist_seq(micropythonify, faketimermanager, monkeypatch):
         fake_mp3.track = None
         dut.onPlaybackDone()
         assert fake_mp3.track is None
+
+
+def test_playlist_unknown_tag(micropythonify, faketimermanager, monkeypatch):
+    class FakeNoPlaylistDb:
+        def getPlaylistForTag(self, tag):
+            return None
+
+    fake_db = FakeNoPlaylistDb()
+    fake_mp3 = FakeMp3Player()
+    deps = app.Dependencies(mp3player=lambda _: fake_mp3,
+                            nfcreader=lambda _: FakeNfcReader(),
+                            buttons=lambda _: FakeButtons(),
+                            playlistdb=lambda _: fake_db)
+    dut = app.PlayerApp(deps)
+    with monkeypatch.context() as m:
+        m.setattr(builtins, 'open', fake_open)
+        dut.onTagChange([23, 42, 1, 2, 3])
+        assert fake_mp3.track is None