Add error message to directory assert

run-exp.py

@@ -41,7 +41,7 @@ class Variable:
 
         if var_type == "file":
             directory = pathlib.Path(value_config["directory"]).expanduser()
-            assert directory.exists() and directory.is_dir()
+            assert directory.exists() and directory.is_dir(), f"No such directory: {directory}"
 
             values = sorted(list(directory.iterdir()))