Source requires_fork through a shim tolerant of where test.support keeps it.

test.support is a private, unversioned corner of the stdlib: its helpers
migrate between the package and its *_helper submodules, and some
distributions ship Python without the test package at all. Look for
requires_fork in each plausible home and approximate it when no home has
one, so the import can't break a supported Python.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Author: jaraco

tests/compat/support.py

@@ -0,0 +1,50 @@
+"""
+``test.support.requires_fork``, defended against a stdlib that keeps it
+somewhere else or not at all.
+
+Relying on ``test.support`` is fine, but it's a private, unversioned corner
+of the stdlib: its helpers migrate between the package and its ``*_helper``
+submodules, and some distributions ship Python without the ``test`` package.
+Prefer whatever the running interpreter supplies and approximate it
+otherwise.
+"""
+
+import contextlib
+import importlib
+import os
+import sys
+import unittest
+
+homes = (
+    'test.support',
+    'test.support.os_helper',
+    'test.support.threading_helper',
+)
+"""
+Modules that host ``requires_fork`` or might plausibly come to host it.
+"""
+
+
+def _supplied():
+    """
+    The stdlib's own ``requires_fork``, wherever it currently lives.
+    """
+    for home in homes:
+        with contextlib.suppress(ImportError, AttributeError):
+            return importlib.import_module(home).requires_fork
+
+
+def _approximated():
+    """
+    Stand in for ``requires_fork`` on a stdlib that doesn't supply one.
+
+    Mirrors ``test.support.has_fork_support``: skip where ``os.fork`` is
+    missing, where subprocesses don't work at all (WASM, Apple mobile), and
+    on Android, where forking is unsafe because every app is threaded.
+    """
+    unsupported = {'emscripten', 'wasi', 'ios', 'tvos', 'watchos', 'android'}
+    supported = hasattr(os, 'fork') and sys.platform not in unsupported
+    return unittest.skipUnless(supported, 'requires working os.fork()')
+
+
+requires_fork = _supplied() or _approximated

tests/test_zip.py

@@ -3,8 +3,6 @@
 import sys
 import unittest
 
-from test.support import requires_fork
-
 from importlib_metadata import (
     FastPath,
     PackageNotFoundError,
@@ -17,6 +15,7 @@
 
 from . import fixtures
 from .compat.py314 import warnings_helper
+from .compat.support import requires_fork
 
 
 class TestZip(fixtures.ZipFixtures, unittest.TestCase):