Ensure PDB cleans up event loop policies after using asyncio.

Author: freakboy3742

Lib/test/test_pdb.py

@@ -13,6 +13,7 @@
 import zipapp
 import zipfile
 
+from asyncio.events import _set_event_loop_policy
 from contextlib import ExitStack, redirect_stdout
 from io import StringIO
 from test import support
@@ -41,6 +42,10 @@ def __exit__(self, *exc):
         if self.orig_trace:
             sys.settrace(self.orig_trace)
 
+        # To prevent a warning "test altered the execution environment" if
+        # asyncio features are used.
+        _set_event_loop_policy(None)
+
 
 def test_pdb_displayhook():
     """This tests the custom displayhook for pdb.