test: add TestSourceMedia & RFE.test_no_input

TestSourceMedia is a mockinobject so

TODO: rename

test/test_feature_extractors.py

@@ -13,6 +13,12 @@ class TestSource():
         SAMPLE_VIDEO = f"{TEST_DIR}/sample_videos/test_video_red_silentaudio.mp4" # silent video definitely has no laughter
         return Source(source=SAMPLE_VIDEO, path=SAMPLE_VIDEO, provider="test")
 
+class TestSourceMedia():
+    """Provide utils.SourceMedia for testing"""
+    def one_colour_silent_audio(self):
+        """Provide a source with a silent mono-colour video"""
+        return SourceMedia(sources=[TestSource().one_colour_silent_audio()])
+
 class TestLaughterFeatureExtractor(unittest.TestCase):
     """Test LaughterFeatureExtractor"""
     def test_init(self):
@@ -39,6 +45,12 @@ class TestRandomFeatureExtractor(unittest.TestCase):
             test_extractor.setup()
         # NB test WITH sources implicitly tested in test_extract
 
+    def test_extract_noinput(self):
+        """Test extract with no input files"""
+        test_extractor = extractors.RandomFeatureExtractor()
+        with self.assertRaises(ValueError):
+            test_extractor.run()
+
     def test_extract(self):
         """Test extract with input files"""
         video_source = TestSourceMedia().one_colour_silent_audio()