bpo-35621: Support running subprocesses in asyncio when loop is executed in non-main thread (#13630)

Lib/test/test_asyncio/test_subprocess.py

@@ -633,6 +633,7 @@ class SubprocessMixin:
 
         self.assertIsNone(self.loop.run_until_complete(execute()))
 
+
 if sys.platform != 'win32':
     # Unix
     class SubprocessWatcherMixin(SubprocessMixin):
@@ -648,7 +649,24 @@ if sys.platform != 'win32':
             watcher = self.Watcher()
             watcher.attach_loop(self.loop)
             policy.set_child_watcher(watcher)
-            self.addCleanup(policy.set_child_watcher, None)
+
+        def tearDown(self):
+            super().setUp()
+            policy = asyncio.get_event_loop_policy()
+            watcher = policy.get_child_watcher()
+            policy.set_child_watcher(None)
+            watcher.attach_loop(None)
+            watcher.close()
+
+    class SubprocessThreadedWatcherTests(SubprocessWatcherMixin,
+                                         test_utils.TestCase):
+
+        Watcher = unix_events.ThreadedChildWatcher
+
+    class SubprocessMultiLoopWatcherTests(SubprocessWatcherMixin,
+                                          test_utils.TestCase):
+
+        Watcher = unix_events.MultiLoopChildWatcher
 
     class SubprocessSafeWatcherTests(SubprocessWatcherMixin,
                                      test_utils.TestCase):
@@ -670,5 +688,25 @@ else:
             self.set_event_loop(self.loop)
 
 
+class GenericWatcherTests:
+
+    def test_create_subprocess_fails_with_inactive_watcher(self):
+
+        async def execute():
+            watcher = mock.create_authspec(asyncio.AbstractChildWatcher)
+            watcher.is_active.return_value = False
+            asyncio.set_child_watcher(watcher)
+
+            with self.assertRaises(RuntimeError):
+                await subprocess.create_subprocess_exec(
+                    support.FakePath(sys.executable), '-c', 'pass')
+
+            watcher.add_child_handler.assert_not_called()
+
+        self.assertIsNone(self.loop.run_until_complete(execute()))
+
+
+
+
 if __name__ == '__main__':
     unittest.main()