bpo-41747: Ensure all dataclass methods uses their parents' qualname (GH-22155)

* bpo-41747: Ensure all dataclass methods uses their parents' qualname

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>
diff --git a/Lib/test/test_dataclasses.py b/Lib/test/test_dataclasses.py
index 7c1d9c5..8887eb6 100644
--- a/Lib/test/test_dataclasses.py
+++ b/Lib/test/test_dataclasses.py
@@ -1936,6 +1936,30 @@ class R:
                     self.assertEqual(new_sample.x, another_new_sample.x)
                     self.assertEqual(sample.y, another_new_sample.y)
 
+    def test_dataclasses_qualnames(self):
+        @dataclass(order=True, unsafe_hash=True, frozen=True)
+        class A:
+            x: int
+            y: int
+
+        self.assertEqual(A.__init__.__name__, "__init__")
+        for function in (
+            '__eq__',
+            '__lt__',
+            '__le__',
+            '__gt__',
+            '__ge__',
+            '__hash__',
+            '__init__',
+            '__repr__',
+            '__setattr__',
+            '__delattr__',
+        ):
+            self.assertEqual(getattr(A, function).__qualname__, f"TestCase.test_dataclasses_qualnames.<locals>.A.{function}")
+
+        with self.assertRaisesRegex(TypeError, r"A\.__init__\(\) missing"):
+            A()
+
 
 class TestFieldNoAnnotation(unittest.TestCase):
     def test_field_without_annotation(self):