gh-116742: Fix subprocess test_check_output_timeout() (#130836)

Fix a race condition in test_check_output_timeout() of
test_subprocess. Don't write into stdout anymore, since there is no
reliable way to synchronize the parent and the child processes.

Change the timeout from 3 seconds to 0.1 seconds, and remove
@requires_resource('walltime') decorator.

Author: vstinner

Lib/test/test_subprocess.py

@@ -269,21 +269,13 @@ def test_check_output_stdin_with_input_arg(self):
         self.assertIn('stdin', c.exception.args[0])
         self.assertIn('input', c.exception.args[0])
 
-    @support.requires_resource('walltime')
     def test_check_output_timeout(self):
         # check_output() function with timeout arg
         with self.assertRaises(subprocess.TimeoutExpired) as c:
             output = subprocess.check_output(
                     [sys.executable, "-c",
-                     "import sys, time\n"
-                     "sys.stdout.write('BDFL')\n"
-                     "sys.stdout.flush()\n"
-                     "time.sleep(3600)"],
-                    # Some heavily loaded buildbots (sparc Debian 3.x) require
-                    # this much time to start and print.
-                    timeout=3)
-            self.fail("Expected TimeoutExpired.")
-        self.assertEqual(c.exception.output, b'BDFL')
+                     "import time; time.sleep(3600)"],
+                    timeout=0.1)
 
     def test_call_kwargs(self):
         # call() function with keyword args
@@ -1694,20 +1686,11 @@ def test_check_output_stdin_with_input_arg(self):
         self.assertIn('stdin', c.exception.args[0])
         self.assertIn('input', c.exception.args[0])
 
-    @support.requires_resource('walltime')
     def test_check_output_timeout(self):
         with self.assertRaises(subprocess.TimeoutExpired) as c:
-            cp = self.run_python((
-                     "import sys, time\n"
-                     "sys.stdout.write('BDFL')\n"
-                     "sys.stdout.flush()\n"
-                     "time.sleep(3600)"),
-                    # Some heavily loaded buildbots (sparc Debian 3.x) require
-                    # this much time to start and print.
-                    timeout=3, stdout=subprocess.PIPE)
-        self.assertEqual(c.exception.output, b'BDFL')
-        # output is aliased to stdout
-        self.assertEqual(c.exception.stdout, b'BDFL')
+            cp = self.run_python(
+                    "import time; time.sleep(3600)",
+                    timeout=0.1, stdout=subprocess.PIPE)
 
     def test_run_kwargs(self):
         newenv = os.environ.copy()