bpo-45678: Add ``functools.singledispatchmethod`` tests (GH-29328) (GH-29390)

(cherry picked from commit 5a14929a6e4fab672e2f83a86773618e973b22a6)

Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>

2 files changed, 43 insertions, 1 deletions

diff --git a/Lib/test/test_functools.py b/Lib/test/test_functools.py
index bdb4ddcc60..1a3c921509 100644
--- a/Lib/test/test_functools.py
+++ b/Lib/test/test_functools.py
@@ -2411,7 +2411,7 @@ class TestSingleDispatch(unittest.TestCase):
         self.assertEqual(A.t(0.0).arg, "base")
 
     def test_abstractmethod_register(self):
-        class Abstract(abc.ABCMeta):
+        class Abstract(metaclass=abc.ABCMeta):
 
             @functools.singledispatchmethod
             @abc.abstractmethod
@@ -2419,6 +2419,10 @@ class TestSingleDispatch(unittest.TestCase):
                 pass
 
         self.assertTrue(Abstract.add.__isabstractmethod__)
+        self.assertTrue(Abstract.__dict__['add'].__isabstractmethod__)
+
+        with self.assertRaises(TypeError):
+            Abstract()
 
     def test_type_ann_register(self):
         class A:
@@ -2479,6 +2483,42 @@ class TestSingleDispatch(unittest.TestCase):
         self.assertEqual(A.t('').arg, "str")
         self.assertEqual(A.t(0.0).arg, "base")
 
+    def test_method_wrapping_attributes(self):
+        class A:
+            @functools.singledispatchmethod
+            def func(self, arg: int) -> str:
+                """My function docstring"""
+                return str(arg)
+            @functools.singledispatchmethod
+            @classmethod
+            def cls_func(cls, arg: int) -> str:
+                """My function docstring"""
+                return str(arg)
+            @functools.singledispatchmethod
+            @staticmethod
+            def static_func(arg: int) -> str:
+                """My function docstring"""
+                return str(arg)
+
+        for meth in (
+            A.func,
+            A().func,
+            A.cls_func,
+            A().cls_func,
+            A.static_func,
+            A().static_func
+        ):
+            with self.subTest(meth=meth):
+                self.assertEqual(meth.__doc__, 'My function docstring')
+                self.assertEqual(meth.__annotations__['arg'], int)
+
+        self.assertEqual(A.func.__name__, 'func')
+        self.assertEqual(A().func.__name__, 'func')
+        self.assertEqual(A.cls_func.__name__, 'cls_func')
+        self.assertEqual(A().cls_func.__name__, 'cls_func')
+        self.assertEqual(A.static_func.__name__, 'static_func')
+        self.assertEqual(A().static_func.__name__, 'static_func')
+
     def test_invalid_registrations(self):
         msg_prefix = "Invalid first argument to `register()`: "
         msg_suffix = (
diff --git a/Misc/NEWS.d/next/Tests/2021-10-30-13-12-20.bpo-45678.bKrYeS.rst b/Misc/NEWS.d/next/Tests/2021-10-30-13-12-20.bpo-45678.bKrYeS.rst
new file mode 100644
index 0000000000..885b2fa64a
--- /dev/null
+++ b/Misc/NEWS.d/next/Tests/2021-10-30-13-12-20.bpo-45678.bKrYeS.rst
@@ -0,0 +1,2 @@
+Add tests to ensure that ``functools.singledispatchmethod`` correctly wraps
+the attributes of the target function.