Adding profiler unit tests

Author: ChrisPaulBennett

cylc/flow/scripts/profiler.py

@@ -27,7 +27,6 @@
 import signal
 from pathlib import Path
 from dataclasses import dataclass
-from typing import Callable, Optional
 from cylc.flow.terminal import cli_function
 from cylc.flow.option_parsers import CylcOptionParser as COP
 
@@ -125,7 +124,8 @@ def get_cgroup_name():
         result = PID_REGEX.search(result).group()
         return result
     except FileNotFoundError as err:
-        raise FileNotFoundError('/proc/' + str(pid) + '/cgroup not found')
+        raise FileNotFoundError(
+            '/proc/' + str(pid) + '/cgroup not found') from err
 
     except AttributeError as err:
         raise AttributeError("No cgroup found for process:", pid) from err