test: add FEFunctionalTest base class for FE tests

Only has a single property at present: SAMPLE_DIR for the path to where
sample videos are stored

TestVideoActivityFEFunctional now inherits from this instead of unittest.TestCase

test/test_feature_extractors_functional.py

@@ -15,7 +15,13 @@ These tests are marked slow to avoid running them during normal test runs.
 import unittest
 import pipeline.feature_extractors as extractors
 import test.mocks as mocks
-class TestVideoActivityFEFunctional(unittest.TestCase):
+
+class FEFunctionalTest(unittest.TestCase):
+    """FEFunctionalTest -- base class for functional tests for feature extractors
+    """
+    SAMPLE_DIR = "/home/robert/code/softdev2023-24/summerproject/highlights/test/sample_videos"
+
+class TestVideoActivityFEFunctional(FEFunctionalTest):
     """TestVisualActivityFEFunctional -- functional tests for visual activity feature extractor
     """
 
@@ -25,7 +31,7 @@ class TestVideoActivityFEFunctional(unittest.TestCase):
         use:
          - sample_videos/sample-manual-visualactivity.mp4 :: activity at 15-20s -- pass if activity detected anywhere in this range
         """
-        SAMPLE_VIDEO = "/home/robert/code/softdev2023-24/summerproject/highlights/test/sample_videos/sample-manual-visualactivity.mp4"
+        SAMPLE_VIDEO = f"{self.SAMPLE_DIR}/sample-manual-visualactivity.mp4"
 
         START_TIME = 15
         END_TIME = 20