test: add negative test for LaughFE

Also rename positive test to indicate that

test/test_feature_extractors_functional.py

@@ -28,7 +28,7 @@ class FEFunctionalTest(unittest.TestCase):
 class TestLaughterFEFunctional(FEFunctionalTest):
     """TestLaughterFEFunctional -- functional tests for laughter detection feature extractor"""
 
-    def test_laughter_detection(self):
+    def test_laughter_detection_positive(self):
         """Test laughter detection feature extractor
 
         Uses:
@@ -61,6 +61,28 @@ class TestLaughterFEFunctional(FEFunctionalTest):
         self.assertTrue(testfe.features[0].interval.start >= (START_TIME - testfe._PREPEND_TIME))
         self.assertTrue(testfe.features[0].interval.end <= (END_TIME + testfe._APPEND_TIME))
 
+    def test_laughter_detection_negative(self):
+        """Negative test for laughter detection feature extractor -- should not detect laughter in a silent video
+
+        Uses:
+            - sample_videos/sample-manual-audio-blank-video-colours.mp4
+              :: silent video (30s)
+                 -- pass iff no laughter features
+        """
+        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.LaughterFeatureExtractor(input_files=[source])
+        testfe.setup()
+        testfe.run()
+        testfe.teardown()
+
+        # check if the feature was extracted:
+        self.assertFalse(testfe.features)
+
 
 class TestVideoActivityFEFunctional(FEFunctionalTest):
     """TestVisualActivityFEFunctional -- functional tests for visual activity feature extractor