gh-139759: Test forking with an unclosed subinterpreter

Port the regression test from #145545.
Wait for the child during cleanup to avoid leaving a zombie process.

Co-authored-by: Aurel Wildfellner <201101774+aurelwildfellner@users.noreply.github.com>

Author: ZeroIntensity

Lib/test/test_interpreters/test_stress.py

@@ -1,9 +1,11 @@
+import os
 import threading
 import unittest
 
 from test import support
 from test.support import import_helper
 from test.support import threading_helper
+from test.support import warnings_helper
 # Raise SkipTest if subinterpreters not supported.
 _interpreters = import_helper.import_module('_interpreters')
 from concurrent import interpreters
@@ -82,6 +84,26 @@ def test_create_interpreter_no_memory(self):
             with support.inject_memory_error_cm(0, 1):
                 _interpreters.create()
 
+    @warnings_helper.ignore_fork_in_thread_deprecation_warnings()
+    @support.requires_fork()
+    def test_unclosed_interpreter_on_fork(self):
+        interp = interpreters.create()
+        interp.exec("pass")
+
+        fds = os.pipe()
+        pid = os.fork()
+
+        if pid == 0:
+            os.close(fds[0])
+            os.write(fds[1], b"OK")
+            os._exit(0)
+        else:
+            os.close(fds[1])
+            self.addCleanup(os.close, fds[0])
+            self.addCleanup(support.wait_process, pid, exitcode=0)
+            value = os.read(fds[0], 100)
+            self.assertEqual(value, b"OK")
+
 
 if __name__ == '__main__':
     # Test needs to be a package, so we can do relative imports.