bpo-43766: Implement PEP 647 (User-Defined Type Guards) in typing.py (#25282)

Lib/test/test_typing.py

@@ -26,6 +26,7 @@ from typing import Pattern, Match
 from typing import Annotated, ForwardRef
 from typing import TypeAlias
 from typing import ParamSpec, Concatenate, ParamSpecArgs, ParamSpecKwargs
+from typing import TypeGuard
 import abc
 import typing
 import weakref
@@ -4377,6 +4378,45 @@ class ConcatenateTests(BaseTestCase):
         self.assertEqual(C4.__parameters__, (T, P))
 
 
+class TypeGuardTests(BaseTestCase):
+    def test_basics(self):
+        TypeGuard[int]  # OK
+
+        def foo(arg) -> TypeGuard[int]: ...
+        self.assertEqual(gth(foo), {'return': TypeGuard[int]})
+
+    def test_repr(self):
+        self.assertEqual(repr(TypeGuard), 'typing.TypeGuard')
+        cv = TypeGuard[int]
+        self.assertEqual(repr(cv), 'typing.TypeGuard[int]')
+        cv = TypeGuard[Employee]
+        self.assertEqual(repr(cv), 'typing.TypeGuard[%s.Employee]' % __name__)
+        cv = TypeGuard[tuple[int]]
+        self.assertEqual(repr(cv), 'typing.TypeGuard[tuple[int]]')
+
+    def test_cannot_subclass(self):
+        with self.assertRaises(TypeError):
+            class C(type(TypeGuard)):
+                pass
+        with self.assertRaises(TypeError):
+            class C(type(TypeGuard[int])):
+                pass
+
+    def test_cannot_init(self):
+        with self.assertRaises(TypeError):
+            TypeGuard()
+        with self.assertRaises(TypeError):
+            type(TypeGuard)()
+        with self.assertRaises(TypeError):
+            type(TypeGuard[Optional[int]])()
+
+    def test_no_isinstance(self):
+        with self.assertRaises(TypeError):
+            isinstance(1, TypeGuard[int])
+        with self.assertRaises(TypeError):
+            issubclass(int, TypeGuard)
+
+
 class AllTests(BaseTestCase):
     """Tests for __all__."""