PYTHON-5874 Fix test_fork.py failures on Python 3.15 due to fork() DeprecationWarning

test/__init__.py

@@ -950,7 +950,17 @@ def _target() -> None:
 
         ctx = multiprocessing.get_context("fork")
         proc = ctx.Process(target=_target)
-        proc.start()
+        # Python 3.12+ warns when os.fork() runs in a multi-threaded process. The
+        # warning is a general thread-count heuristic; benign here because the only
+        # extra threads are pymongo's, whose locks are reset via register_at_fork
+        # in the child. Suppressed only in this helper, not globally (PYTHON-5874).
+        with warnings.catch_warnings():
+            warnings.filterwarnings(
+                "ignore",
+                message=r".*use of fork\(\) may lead to deadlocks.*",
+                category=DeprecationWarning,
+            )
+            proc.start()
         try:
             yield proc  # type: ignore
         finally:

test/asynchronous/__init__.py

@@ -950,7 +950,17 @@ def _target() -> None:
 
         ctx = multiprocessing.get_context("fork")
         proc = ctx.Process(target=_target)
-        proc.start()
+        # Python 3.12+ warns when os.fork() runs in a multi-threaded process. The
+        # warning is a general thread-count heuristic; benign here because the only
+        # extra threads are pymongo's, whose locks are reset via register_at_fork
+        # in the child. Suppressed only in this helper, not globally (PYTHON-5874).
+        with warnings.catch_warnings():
+            warnings.filterwarnings(
+                "ignore",
+                message=r".*use of fork\(\) may lead to deadlocks.*",
+                category=DeprecationWarning,
+            )
+            proc.start()
         try:
             yield proc  # type: ignore
         finally:

test/test_fork.py

@@ -29,17 +29,15 @@
 from test.utils_shared import is_greenthread_patched
 
 
+# self.fork suppresses the Python 3.12+ fork() DeprecationWarning; it is
+# benign for these intentional forks (PYTHON-5874).
 @unittest.skipIf(
     not hasattr(os, "register_at_fork"), "register_at_fork not available in this version of Python"
 )
 @unittest.skipIf(
     is_greenthread_patched(),
     "gevent does not support POSIX-style forking.",
 )
-@unittest.skipIf(
-    sys.version_info >= (3, 15),
-    "fork() in multi-threaded processes is deprecated in Python 3.15+ (PYTHON-5874)",
-)
 class TestFork(IntegrationTest):
     def test_lock_client(self):
         # Forks the client with some items locked.