gh-155027: Make test_asyncio's socket harness able to fail a test

Lib/test/test_asyncio/functional.py

@@ -28,6 +28,7 @@ def setUp(self):
 
         self.loop.set_exception_handler(self.loop_exception_handler)
         self.__unhandled_exceptions = []
+        self.__abort_exception = None
 
     def tearDown(self):
         try:
@@ -38,9 +39,13 @@ def tearDown(self):
                 pprint.pprint(self.__unhandled_exceptions)
                 self.fail('unexpected calls to loop.call_exception_handler()')
 
+            if self.__abort_exception is not None:
+                raise self.__abort_exception
+
         finally:
             asyncio.set_event_loop(None)
             self.loop = None
+            self.__abort_exception = None
 
     def tcp_server(self, server_prog, *,
                    family=socket.AF_INET,
@@ -104,10 +109,18 @@ def unix_sock_name(self):
                     pass
 
     def _abort_socket_test(self, ex):
+        # This runs in the client/server thread, not the main thread, so
+        # it must not call self.fail(): the AssertionError would escape
+        # Thread.run() without failing the test. Stash the exception and
+        # let tearDown() re-raise it on the main thread.
         try:
-            self.loop.stop()
+            self.loop.call_soon_threadsafe(self.loop.stop)
+        except RuntimeError:
+            # The loop is already closed; nothing left to stop.
+            pass
         finally:
-            self.fail(ex)
+            if self.__abort_exception is None:
+                self.__abort_exception = ex
 
 
 ##############################################################################

Misc/NEWS.d/next/Tests/2026-08-01-10-30-00.gh-issue-155027.Kq7Wm2.rst

@@ -0,0 +1,7 @@
+Fix ``test_asyncio``'s socket test harness so that a failure in the client
+or server thread actually fails the test.  ``_abort_socket_test()`` called
+``self.fail()`` from a worker thread, where the resulting
+:exc:`AssertionError` cannot fail the test; it now records the exception and
+re-raises it on the main thread.  It also stops the event loop with
+:meth:`~asyncio.loop.call_soon_threadsafe` rather than calling
+:meth:`~asyncio.loop.stop` directly from a non-main thread.