Update testing.py

there was a change in Python 3.10 and the Mapping class has been moved to the collections.abc module. So, if you're using Python 3.10 or later, you should import the Mapping class from the collections.abc module, not the collections module

fastreid/evaluation/testing.py

@@ -2,7 +2,8 @@
 import logging
 import pprint
 import sys
-from collections import Mapping, OrderedDict
+from collections import OrderedDict
+from collections.abc import Mapping
 
 import numpy as np
 from tabulate import tabulate