bpo-30149: Fix partialmethod without explicit self parameter (#1308) (#1662)

diff --git a/Lib/test/test_inspect.py b/Lib/test/test_inspect.py
index 37e4511..facf040 100644
--- a/Lib/test/test_inspect.py
+++ b/Lib/test/test_inspect.py
@@ -1989,6 +1989,41 @@
                            ('kwargs', ..., int, "var_keyword")),
                           ...))
 
+    def test_signature_without_self(self):
+        def test_args_only(*args):  # NOQA
+            pass
+
+        def test_args_kwargs_only(*args, **kwargs):  # NOQA
+            pass
+
+        class A:
+            @classmethod
+            def test_classmethod(*args):  # NOQA
+                pass
+
+            @staticmethod
+            def test_staticmethod(*args):  # NOQA
+                pass
+
+            f1 = functools.partialmethod((test_classmethod), 1)
+            f2 = functools.partialmethod((test_args_only), 1)
+            f3 = functools.partialmethod((test_staticmethod), 1)
+            f4 = functools.partialmethod((test_args_kwargs_only),1)
+
+        self.assertEqual(self.signature(test_args_only),
+                         ((('args', ..., ..., 'var_positional'),), ...))
+        self.assertEqual(self.signature(test_args_kwargs_only),
+                         ((('args', ..., ..., 'var_positional'),
+                           ('kwargs', ..., ..., 'var_keyword')), ...))
+        self.assertEqual(self.signature(A.f1),
+                         ((('args', ..., ..., 'var_positional'),), ...))
+        self.assertEqual(self.signature(A.f2),
+                         ((('args', ..., ..., 'var_positional'),), ...))
+        self.assertEqual(self.signature(A.f3),
+                         ((('args', ..., ..., 'var_positional'),), ...))
+        self.assertEqual(self.signature(A.f4), 
+                         ((('args', ..., ..., 'var_positional'),
+                            ('kwargs', ..., ..., 'var_keyword')), ...))
     @cpython_only
     @unittest.skipIf(MISSING_C_DOCSTRINGS,
                      "Signature information for builtins requires docstrings")