Skip a problematic test on CPython 3.12.0b1 (#200)

Author: AlexWaygood

CHANGELOG.md

@@ -1,3 +1,9 @@
+# Unreleased
+
+- Skip a problematic test on Python 3.12.0b1. The test fails on 3.12.0b1 due to
+  a bug in CPython, which will be fixed in 3.12.0b2. The
+  `typing_extensions` test suite now passes on 3.12.0b1.
+
 # Release 4.6.2 (May 25, 2023)
 
 - Fix use of `@deprecated` on classes with `__new__` but no `__init__`.

src/test_typing_extensions.py

@@ -2267,6 +2267,10 @@ class Foo: ...
         del f.x
         self.assertNotIsInstance(f, HasX)
 
+    @skipIf(
+        sys.version_info == (3, 12, 0, 'beta', 1),
+        "CPython had a bug in 3.12.0b1"
+    )
     def test_protocols_isinstance_generic_classes(self):
         T = TypeVar("T")