bpo-33582: Emit deprecation warning for `formatargspec` (GH-6994)

(cherry picked from commit 46c5cd0f6e22bdfbdd3f0b18f1d01eda754e7e11)

Co-authored-by: Matthias Bussonnier <bussonniermatthias@gmail.com>
diff --git a/Lib/test/test_inspect.py b/Lib/test/test_inspect.py
index ff6f014..8b70161 100644
--- a/Lib/test/test_inspect.py
+++ b/Lib/test/test_inspect.py
@@ -712,8 +712,9 @@
         self.assertEqual(varkw, varkw_e)
         self.assertEqual(defaults, defaults_e)
         if formatted is not None:
-            self.assertEqual(inspect.formatargspec(args, varargs, varkw, defaults),
-                             formatted)
+            with self.assertWarns(DeprecationWarning):
+                self.assertEqual(inspect.formatargspec(args, varargs, varkw, defaults),
+                                 formatted)
 
     def assertFullArgSpecEquals(self, routine, args_e, varargs_e=None,
                                     varkw_e=None, defaults_e=None,
@@ -729,8 +730,9 @@
         self.assertEqual(kwonlydefaults, kwonlydefaults_e)
         self.assertEqual(ann, ann_e)
         if formatted is not None:
-            self.assertEqual(inspect.formatargspec(args, varargs, varkw, defaults,
-                                                    kwonlyargs, kwonlydefaults, ann),
+            with self.assertWarns(DeprecationWarning):
+                self.assertEqual(inspect.formatargspec(args, varargs, varkw, defaults,
+                                                       kwonlyargs, kwonlydefaults, ann),
                              formatted)
 
     def test_getargspec(self):