[3.10] Fix warning: asyncio.events._event_loop_policy was modified by test_asyncio (GH-31253) (GH-31255)

(cherry picked from commit 012e77eb5c)

Co-authored-by: Andrew Svetlov <andrew.svetlov@gmail.com>

Lib/test/test_asyncio/test_futures2.py

@@ -3,6 +3,10 @@
 import unittest
 
 
+def tearDownModule():
+    asyncio.set_event_loop_policy(None)
+
+
 class FutureTests(unittest.IsolatedAsyncioTestCase):
     async def test_recursive_repr_for_pending_tasks(self):
         # The call crashes if the guard for recursive call

Lib/test/test_asyncio/test_protocols.py

@@ -4,6 +4,12 @@
 import asyncio
 
 
+def tearDownModule():
+    # not needed for the test file but added for uniformness with all other
+    # asyncio test files for the sake of unified cleanup
+    asyncio.set_event_loop_policy(None)
+
+
 class ProtocolsAbsTests(unittest.TestCase):
 
     def test_base_protocol(self):

Lib/test/test_asyncio/test_runners.py

@@ -5,6 +5,10 @@
 from test.test_asyncio import utils as test_utils
 
 
+def tearDownModule():
+    asyncio.set_event_loop_policy(None)
+
+
 class TestPolicy(asyncio.AbstractEventLoopPolicy):
 
     def __init__(self, loop_factory):

Lib/test/test_asyncio/test_sock_lowlevel.py

@@ -10,6 +10,10 @@
 from test.support import socket_helper
 
 
+def tearDownModule():
+    asyncio.set_event_loop_policy(None)
+
+
 class MyProto(asyncio.Protocol):
     connected = None
     done = None

Lib/test/test_asyncio/test_transports.py

@@ -7,6 +7,12 @@
 from asyncio import transports
 
 
+def tearDownModule():
+    # not needed for the test file but added for uniformness with all other
+    # asyncio test files for the sake of unified cleanup
+    asyncio.set_event_loop_policy(None)
+
+
 class TransportTests(unittest.TestCase):
 
     def test_ctor_extra_is_none(self):

Lib/test/test_asyncio/test_unix_events.py

@@ -26,6 +26,10 @@
 from test.test_asyncio import utils as test_utils
 
 
+def tearDownModule():
+    asyncio.set_event_loop_policy(None)
+
+
 MOCK_ANY = mock.ANY
 
 
@@ -39,10 +43,6 @@ def SIGNAL(signum):
     return 32768 - signum
 
 
-def tearDownModule():
-    asyncio.set_event_loop_policy(None)
-
-
 def close_pipe_transport(transport):
     # Don't call transport.close() because the event loop and the selector
     # are mocked

Misc/NEWS.d/next/Tests/2022-02-10-14-33-47.bpo-46708.avLfCb.rst

@@ -0,0 +1,2 @@
+Prevent default asyncio event loop policy modification warning after
+``test_asyncio`` execution.