gh-151540: Use a selector event loop in the happy-eyeballs tests

test_create_connection_happy_eyeballs and
test_create_connection_happy_eyeballs_ipv4_only used
asyncio.new_event_loop(), which defaults to ProactorEventLoop on
Windows. Creating a socket transport on that loop registers the
mocked socket with a real I/O completion port, bypassing the
mocked _add_reader/_add_writer and failing in a callback with
"TypeError: an integer is required" because MagicMock.fileno()
does not return an int.

Use asyncio.SelectorEventLoop() explicitly instead, matching the
code path these tests already exercise on non-Windows platforms.

Author: jmrossi98

Lib/test/test_asyncio/test_base_events.py

@@ -1092,7 +1092,11 @@ async def sock_connect(sock, address):
                 await asyncio.sleep(1)
             sock.connect(address)
 
-        loop = asyncio.new_event_loop()
+        # gh-151540: use a selector event loop instead of the platform
+        # default; the Windows proactor loop would register the mocked
+        # socket with a real IOCP handle instead of the mocked
+        # _add_reader/_add_writer below.
+        loop = asyncio.SelectorEventLoop()
         loop._add_writer = mock.Mock()
         loop._add_writer = mock.Mock()
         loop._add_reader = mock.Mock()
@@ -1124,7 +1128,8 @@ async def sock_connect(sock, address):
                 await asyncio.sleep(1)
             sock.connect(address)
 
-        loop = asyncio.new_event_loop()
+        # gh-151540: see test_create_connection_happy_eyeballs above.
+        loop = asyncio.SelectorEventLoop()
         loop._add_writer = mock.Mock()
         loop._add_writer = mock.Mock()
         loop._add_reader = mock.Mock()

Misc/NEWS.d/next/Tests/2026-07-08-21-45-00.gh-issue-151540.pQx3Wm.rst

@@ -0,0 +1,5 @@
+Fix the happy-eyeballs tests in ``test.test_asyncio.test_base_events``
+raising ``TypeError`` in a callback on Windows. The tests now use a
+selector event loop explicitly instead of the platform default, as the
+Windows proactor event loop registers the mocked test socket with a real
+I/O completion port.