refactor: simplify music metadata processing by removing unused code and improving album signal detection

app/tests/test_ytdl_utils.py

@@ -31,10 +31,6 @@ class _PostProcessor:
         self._downloader = downloader
 
 
-class _PostProcessingError(Exception):
-    pass
-
-
 fake_impersonate.ImpersonateTarget = _ImpersonateTarget
 fake_networking.impersonate = fake_impersonate
 fake_postprocessor_common.PostProcessor = _PostProcessor
@@ -43,7 +39,6 @@ fake_postprocessor_common.PostProcessor = _PostProcessor
 # ``_resolve_outtmpl_fields`` reads via ``match.group('key')``.
 fake_utils.STR_FORMAT_RE_TMPL = r"(?P<prefix>)%\((?P<has_key>(?P<key>{}))\)(?P<format>[-0-9.]*{})"
 fake_utils.STR_FORMAT_TYPES = "diouxXeEfFgGcrsa"
-fake_utils.PostProcessingError = _PostProcessingError
 fake_yt_dlp.networking = fake_networking
 fake_yt_dlp.postprocessor = fake_postprocessor
 fake_yt_dlp.utils = fake_utils
@@ -58,7 +53,6 @@ from ytdl import (
     Download,
     DownloadInfo,
     MusicMetadataPreProcessor,
-    MusicMetadataWriterPostProcessor,
     _compact_persisted_entry,
     _convert_srt_to_txt_file,
     _AlbumArtistPostProcessor,
@@ -193,10 +187,7 @@ class AlbumArtistRegistrationTests(unittest.TestCase):
         metadata_preprocessor, = metadata_pre_call.args
         self.assertIsInstance(metadata_preprocessor, MusicMetadataPreProcessor)
         self.assertEqual(metadata_pre_call.kwargs, {'when': 'pre_process'})
-        metadata_writer_call = fake_ydl.add_post_processor.call_args_list[2]
-        metadata_writer, = metadata_writer_call.args
-        self.assertIsInstance(metadata_writer, MusicMetadataWriterPostProcessor)
-        self.assertEqual(metadata_writer_call.kwargs, {'when': 'after_move'})
+        self.assertEqual(fake_ydl.add_post_processor.call_count, 2)
 
     def test_video_download_does_not_register_postprocessor(self):
         download = _make_test_download()