Address review

Author: sobolevn

Doc/library/mimetypes.rst

@@ -134,7 +134,7 @@ behavior of the module.
    When *strict* is ``True`` (the default), the mapping will be added to the
    official MIME types, otherwise to the non-standard ones.
 
-   .. versionchanged:: 3.14
+   .. deprecated:: 3.14
       *ext* values that do not start with ``'.'`` are deprecated.
 
    .. versionchanged:: next

Lib/mimetypes.py

@@ -93,10 +93,7 @@ def add_type(self, type, ext, strict=True):
         Valid extensions are empty or start with a '.'.
         """
         if ext and not ext.startswith('.'):
-            raise ValueError(
-                "Adding an extension without a leading dot "
-                f"{ext!r} is not supported"
-            )
+            raise ValueError(f"Extension {ext!r} must start with '.'")
 
         if not type:
             return

Lib/test/test_mimetypes.py

@@ -390,19 +390,10 @@ def test_added_types_are_used(self):
         self.assertEqual(mime_type, 'testing/type')
 
     def test_add_type_with_undotted_extension_not_supported(self):
-        msg = (
-            "Adding an extension without a leading dot "
-            "'undotted' is not supported"
-        )
-        with self.assertRaisesRegex(
-            ValueError,
-            msg,
-        ):
+        msg = "Extension 'undotted' must start with '.'"
+        with self.assertRaisesRegex(ValueError, msg):
             mimetypes.add_type("testing/type", "undotted")
-        with self.assertRaisesRegex(
-            ValueError,
-            msg,
-        ):
+        with self.assertRaisesRegex(ValueError, msg):
             mimetypes.add_type("", "undotted")