fix the _namespace_map cleanup for cElementTree tests.
diff --git a/Lib/xml/etree/ElementTree.py b/Lib/xml/etree/ElementTree.py
index 93147eb..defef0d 100644
--- a/Lib/xml/etree/ElementTree.py
+++ b/Lib/xml/etree/ElementTree.py
@@ -1086,6 +1086,8 @@
     # dublin core
     "http://purl.org/dc/elements/1.1/": "dc",
 }
+# For tests and troubleshooting
+register_namespace._namespace_map = _namespace_map
 
 def _raise_serialization_error(text):
     raise TypeError(