closes bpo-38692: Add a pidfd child process watcher to asyncio. (GH-17069)

Lib/test/test_asyncio/test_subprocess.py

@@ -1,3 +1,4 @@
+import os
 import signal
 import sys
 import unittest
@@ -691,6 +692,23 @@ if sys.platform != 'win32':
 
         Watcher = unix_events.FastChildWatcher
 
+    def has_pidfd_support():
+        if not hasattr(os, 'pidfd_open'):
+            return False
+        try:
+            os.close(os.pidfd_open(os.getpid()))
+        except OSError:
+            return False
+        return True
+
+    @unittest.skipUnless(
+        has_pidfd_support(),
+        "operating system does not support pidfds",
+    )
+    class SubprocessPidfdWatcherTests(SubprocessWatcherMixin,
+                                      test_utils.TestCase):
+        Watcher = unix_events.PidfdChildWatcher
+
 else:
     # Windows
     class SubprocessProactorTests(SubprocessMixin, test_utils.TestCase):