gh-145754: Update signature retrieval in unittest.mock to use forwardref annotation format

Lib/test/test_unittest/testmock/testmock.py

@@ -1743,6 +1743,17 @@ def static_method(): pass
                 mock_method.assert_called_once_with()
                 self.assertRaises(TypeError, mock_method, 'extra_arg')
 
+    #Issue145754
+    def test_create_autospec_type_hints_typechecking(self):
+        from typing import TYPE_CHECKING
+        if TYPE_CHECKING:
+            from typing import Tuple
+
+        def foo(x: Tuple[int, ...]) -> None:
+            pass
+
+        mock.create_autospec(foo)
+
     #Issue21238
     def test_mock_unsafe(self):
         m = Mock()

Lib/unittest/mock.py

@@ -34,6 +34,7 @@
 import pkgutil
 from inspect import iscoroutinefunction
 import threading
+from annotationlib import Format
 from dataclasses import fields, is_dataclass
 from types import CodeType, ModuleType, MethodType
 from unittest.util import safe_repr
@@ -119,7 +120,7 @@ def _get_signature_object(func, as_instance, eat_self):
     else:
         sig_func = func
     try:
-        return func, inspect.signature(sig_func)
+        return func, inspect.signature(sig_func, annotation_format=Format.FORWARDREF)
     except ValueError:
         # Certain callable types are not supported by inspect.signature()
         return None

Misc/NEWS.d/next/Library/2026-03-10-14-57-15.gh-issue-145754.YBL5Ko.rst

@@ -0,0 +1,3 @@
+Request signature during mock autospec with ``FORWARDREF`` annotation format.
+This prevents runtime errors when a type referred in a type hint is
+imported within a ``TYPE_CHECKING`` block.