bpo-46414: Add typing.reveal_type (#30646)

Co-authored-by: Nikita Sobolev <mail@sobolevn.me>

Lib/test/test_typing.py

@@ -20,6 +20,7 @@ from typing import cast, runtime_checkable
 from typing import get_type_hints
 from typing import get_origin, get_args
 from typing import is_typeddict
+from typing import reveal_type
 from typing import no_type_check, no_type_check_decorator
 from typing import Type
 from typing import NamedTuple, TypedDict
@@ -34,7 +35,7 @@ import typing
 import weakref
 import types
 
-from test.support import import_helper
+from test.support import import_helper, captured_stderr
 from test import mod_generics_cache
 from test import _typed_dict_helper
 
@@ -5289,6 +5290,14 @@ class SpecialAttrsTests(BaseTestCase):
         self.assertIn('baz', dir(Foo[int]))
 
 
+class RevealTypeTests(BaseTestCase):
+    def test_reveal_type(self):
+        obj = object()
+        with captured_stderr() as stderr:
+            self.assertIs(obj, reveal_type(obj))
+        self.assertEqual(stderr.getvalue(), "Runtime type is 'object'\n")
+
+
 class AllTests(BaseTestCase):
     """Tests for __all__."""