Add fallback for old packaging

setup.cfg

@@ -89,7 +89,7 @@ testing-integration =
 	jaraco.envs>=2.2
 	build[virtualenv]>=1.0.3
 	filelock>=3.4.0
-	packaging
+	packaging>=23.1  # TODO: update once packaging 23.2 is available
 
 docs =
 	# upstream

setuptools/tests/_packaging_compat.py

@@ -0,0 +1,9 @@
+from packaging import __version__ as packaging_version
+
+if tuple(packaging_version.split(".")) >= ("23", "2"):
+    from packaging.metadata import Metadata
+else:
+    # Just pretend it exists while waiting for release...
+    from unittest.mock import MagicMock
+
+    Metadata = MagicMock()

setuptools/tests/config/test_apply_pyprojecttoml.py

@@ -13,7 +13,9 @@
 
 import pytest
 from ini2toml.api import Translator
-from packaging.metadata import Metadata
+
+# TODO: replace with `from packaging.metadata import Metadata` in future versions
+from .._packaging_compat import Metadata
 
 import setuptools  # noqa ensure monkey patch to metadata
 from setuptools.dist import Distribution

setuptools/tests/test_core_metadata.py

@@ -5,7 +5,8 @@
 
 import pytest
 
-from packaging.metadata import Metadata
+# TODO: replace with `from packaging.metadata import Metadata` in future versions:
+from ._packaging_compat import Metadata
 
 from setuptools import sic, _reqs
 from setuptools.dist import Distribution