Use patlib.Path in tests and tools

bin/run_tests.py

@@ -3,10 +3,11 @@
 import os
 import subprocess
 import sys
+from pathlib import Path
 
 if __name__ == '__main__':
     # move cwd to the project root
-    os.chdir(os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
+    os.chdir(Path(__file__).resolve().parents[1])
 
     # run the unit tests
     subprocess.check_call([sys.executable, '-m', 'pytest', 'unit_test'])