test: add negative test to TestLoudAudioFEFunctional

Video file with silent audio (generated with sox) -- should produce no features
since "-inf" are filtered by the FE

test/test_feature_extractors_functional.py

@@ -86,6 +86,28 @@ class TestLoudAudioFEFunctional(FEFunctionalTest):
         # check if the highest scoring feature is within the peak range
         self.assertTrue(sorted_features[0].interval.start >= PEAK_START)
 
+    def test_audio_loudness_functional_no_features(self):
+        """Test audio loudness feature extractor using a silent video. This should produce no features
+        since "-inf" results from pyloudnorm are filtered out by the FE.
+
+        Use:
+         - sample_videos/sample-manual-audio-blank-video-colours.mp4
+           :: silent video (30s)
+              -- pass if no features extracted
+        """
+        SAMPLE_VIDEO = f"{self.SAMPLE_DIR}/sample-manual-audio-blank-video-colours.mp4"
+
+        # create mock source with the video
+        source = mocks.MockSource(path=SAMPLE_VIDEO)
+
+        # create the feature extractor
+        testfe = extractors.LoudAudioFeatureExtractor(input_files=[source])
+        testfe.setup()
+        testfe.run()
+        testfe.teardown()
+
+        # check if the feature was extracted:
+        self.assertFalse(testfe.features)
 
 
 if __name__ == "__main__":