bpo-46480: add typing.assert_type (GH-30843)

Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>
Co-authored-by: David Foster <david@dafoster.net>

1 files changed, 17 insertions, 1 deletions

diff --git a/Lib/test/test_typing.py b/Lib/test/test_typing.py
index b212b523048..e88f7322b2f 100644
--- a/Lib/test/test_typing.py
+++ b/Lib/test/test_typing.py
@@ -16,7 +16,7 @@ from typing import Union, Optional, Literal
 from typing import Tuple, List, Dict, MutableMapping
 from typing import Callable
 from typing import Generic, ClassVar, Final, final, Protocol
-from typing import cast, runtime_checkable
+from typing import assert_type, cast, runtime_checkable
 from typing import get_type_hints
 from typing import get_origin, get_args
 from typing import is_typeddict
@@ -3302,6 +3302,22 @@ class CastTests(BaseTestCase):
         cast('hello', 42)
 
 
+class AssertTypeTests(BaseTestCase):
+
+    def test_basics(self):
+        arg = 42
+        self.assertIs(assert_type(arg, int), arg)
+        self.assertIs(assert_type(arg, str | float), arg)
+        self.assertIs(assert_type(arg, AnyStr), arg)
+        self.assertIs(assert_type(arg, None), arg)
+
+    def test_errors(self):
+        # Bogus calls are not expected to fail.
+        arg = 42
+        self.assertIs(assert_type(arg, 42), arg)
+        self.assertIs(assert_type(arg, 'hello'), arg)
+
+
 # We need this to make sure that `@no_type_check` respects `__module__` attr:
 from test import ann_module8