Capture expectations about _normalized_name compatibility in test

Author: abravalheri

tests/test_integration.py

@@ -1,3 +1,5 @@
+import sys
+import pathlib
 import unittest
 import packaging.requirements
 import packaging.version
@@ -6,7 +8,10 @@
 from importlib_metadata import (
     MetadataPathFinder,
     _compat,
+    distribution,
     distributions,
+    entry_points,
+    metadata,
     version,
 )
 
@@ -43,6 +48,48 @@ def __getattribute__(self, name):
         _compat.disable_stdlib_finder()
 
 
+class OldStdlibFinderTests(fixtures.DistInfoPkgOffPath, unittest.TestCase):
+    def setUp(self):
+        python_version = sys.version_info[:2]
+        if python_version < (3, 8) or python_version > (3, 9):
+            self.skipTest("Tests specific for Python 3.8/3.9")
+        super().setUp()
+
+    def _meta_path_finder(self):
+        from importlib.metadata import DistributionFinder, PathDistribution
+        from importlib.util import spec_from_file_location
+
+        path = pathlib.Path(self.site_dir)
+
+        class CustomFinder:
+            @classmethod
+            def find_spec(cls, fullname, _path=None, _target=None):
+                candidate = pathlib.Path(path, *fullname.split(".")).with_suffix(".py")
+                if candidate.exists():
+                    return spec_from_file_location(fullname, candidate)
+
+            @classmethod
+            def find_distributions(self, context=DistributionFinder.Context()):
+                for dist_info in path.glob("*.dist-info"):
+                    yield PathDistribution(dist_info)
+
+        return CustomFinder
+
+    def test_compatibility_with_old_stdlib_path_distribution(self):
+        """
+        Given a custom finder that uses Python 3.8/3.9 importlib.metadata is installed,
+        when importlib_metadata functions are called, there should be no exceptions.
+        Ref python/importlib_metadata#396.
+        """
+        self.fixtures.enter_context(fixtures.install_finder(self._meta_path_finder()))
+
+        assert list(distributions())
+        assert distribution("distinfo_pkg")
+        assert version("distinfo_pkg") > "0"
+        assert list(metadata("distinfo_pkg"))
+        assert list(entry_points(group="entries"))
+
+
 class DistSearch(unittest.TestCase):
     def test_search_dist_dirs(self):
         """