replaygain: apply review feedback: fixup previous refactor, improve tests

by adding files which are not completely silent, thus hitting a different
code path in some calculations

The sample files were generated using
> sox -n whitenoise.flac synth 00:00:02 whitenoise
> ffmpeg -i whitenoise.flac whitenoise.opus
> ffmpeg -i whitenoise.flac whitenoise.mp3

beetsplug/replaygain.py

@@ -329,7 +329,7 @@ class FfmpegBackend(Backend):
 
         def sum_of_track_powers(track_gain, track_n_blocks):
             # convert `LU to target_level` -> LUFS
-            loudness = target_level_lufs - track_gain
+            loudness = target_level_lufs - track_gain.gain
 
             # This reverses ITU-R BS.1770-4 p. 6 equation (5) to convert
             # from loudness to power. The result is the average gating
@@ -586,7 +586,7 @@ class CommandBackend(Backend):
         When computing album gain, the last TrackGain object returned is
         the album gain
         """
-        if len(items) == 0:
+        if not items:
             self._log.debug('no supported tracks to analyze')
             return []
 
@@ -1375,7 +1375,7 @@ class ReplayGainPlugin(BeetsPlugin):
             pass
 
     def close_pool(self):
-        """Regularly lose the `ThreadPool` instance in `self.pool`.
+        """Regularly close the `ThreadPool` instance in `self.pool`.
         """
         if self.pool is not None:
             self.pool.close()

test/helper.py

@@ -373,11 +373,20 @@ class TestHelper:
             items.append(item)
         return items
 
-    def add_album_fixture(self, track_count=1, ext='mp3', disc_count=1):
+    def add_album_fixture(
+        self,
+        track_count=1,
+        fname='full',
+        ext='mp3',
+        disc_count=1,
+    ):
         """Add an album with files to the database.
         """
         items = []
-        path = os.path.join(_common.RSRC, util.bytestring_path('full.' + ext))
+        path = os.path.join(
+            _common.RSRC,
+            util.bytestring_path(f'{fname}.{ext}'),
+        )
         for discnumber in range(1, disc_count + 1):
             for i in range(track_count):
                 item = Item.from_path(path)

test/test_replaygain.py

@@ -85,6 +85,8 @@ class FfmpegBackendMixin():
 
 
 class ReplayGainCliTestBase(TestHelper):
+    FNAME: str
+
     def setUp(self):
         # Implemented by Mixins, see above. This may decide to skip the test.
         self.test_backend()
@@ -99,7 +101,8 @@ class ReplayGainCliTestBase(TestHelper):
             self.unload_plugins()
 
     def _add_album(self, *args, **kwargs):
-        album = self.add_album_fixture(*args, **kwargs)
+        # Use a file with non-zero volume (most test assets are total silence)
+        album = self.add_album_fixture(*args, fname=self.FNAME, **kwargs)
         for item in album.items():
             reset_replaygain(item)
 
@@ -305,19 +308,25 @@ class ReplayGainCliTestBase(TestHelper):
 @unittest.skipIf(not GST_AVAILABLE, 'gstreamer cannot be found')
 class ReplayGainGstCliTest(ReplayGainCliTestBase, unittest.TestCase,
                            GstBackendMixin):
-    pass
+    FNAME = "full"  # file contains only silence
 
 
 @unittest.skipIf(not GAIN_PROG_AVAILABLE, 'no *gain command found')
 class ReplayGainCmdCliTest(ReplayGainCliTestBase, unittest.TestCase,
                            CmdBackendMixin):
-    pass
+    FNAME = "full"  # file contains only silence
 
 
 @unittest.skipIf(not FFMPEG_AVAILABLE, 'ffmpeg cannot be found')
 class ReplayGainFfmpegCliTest(ReplayGainCliTestBase, unittest.TestCase,
                               FfmpegBackendMixin):
-    pass
+    FNAME = "full"  # file contains only silence
+
+
+@unittest.skipIf(not FFMPEG_AVAILABLE, 'ffmpeg cannot be found')
+class ReplayGainFfmpegNoiseCliTest(ReplayGainCliTestBase, unittest.TestCase,
+                                   FfmpegBackendMixin):
+    FNAME = "whitenoise"
 
 
 class ImportTest(TestHelper):