Add tests

Author: johnslavik

Lib/test/test_functools.py

@@ -3005,6 +3005,56 @@ def static_func(arg: int) -> str:
         self.assertEqual(A.static_func.__name__, 'static_func')
         self.assertEqual(A().static_func.__name__, 'static_func')
 
+    def test_method_classlevel_calls(self):
+        """Regression test for GH-144615."""
+        class C:
+            @functools.singledispatchmethod
+            def generic(self, x: object):
+                return "generic"
+
+            @generic.register
+            def special1(self, x: int):
+                return "special1"
+
+            @generic.register
+            @classmethod
+            def special2(self, x: float):
+                return "special2"
+
+            @generic.register
+            @staticmethod
+            def special3(self, x: complex):
+                return "special3"
+
+            def special4(self, x):
+                return "special4"
+
+            class D1:
+                def __get__(self, _, owner):
+                    return lambda inst, x: owner.special4(inst, x)
+
+            generic.register(D1, D1())
+
+            def special5(self, x):
+                return "special5"
+
+            class D2:
+                def __get__(self, inst, owner):
+                    # Different instance bound to the returned method
+                    # doesn't cause it to receive the original instance
+                    # as a separate argument. Return a partial() to workaround.
+                    return C().special5
+
+            generic.register(D2, D2())
+
+
+        self.assertEqual(C.generic(C(), "foo"), "generic")
+        self.assertEqual(C.generic(C(), 1), "special1")
+        self.assertEqual(C.generic(C(), 2.0), "special2")
+        self.assertEqual(C.generic(C(), 3j), "special3")
+        self.assertEqual(C.generic(C(), C.D1()), "special4")
+        self.assertEqual(C.generic(C(), C.D2()), "special5")
+
     def test_method_repr(self):
         class Callable:
             def __call__(self, *args):