Add test capturing expectation that users should receive a hint as to the cause of a PackageNotFoundError if the package metadata is missing. Ref #124.

Author: jaraco

importlib_metadata/tests/test_main.py

@@ -35,6 +35,18 @@ def test_for_name_does_not_exist(self):
         with self.assertRaises(PackageNotFoundError):
             Distribution.from_name('does-not-exist')
 
+    def test_package_not_found_mentions_metadata(self):
+        """
+        When a package is not found, that could indicate that the
+        packgae is not installed or that it is installed without
+        metadata. Ensure the exception mentions metadata to help
+        guide users toward the cause. See #124.
+        """
+        with self.assertRaises(PackageNotFoundError) as ctx:
+            Distribution.from_name('does-not-exist')
+
+        assert "metadata" in str(ctx.exception)
+
     def test_new_style_classes(self):
         self.assertIsInstance(Distribution, type)
         self.assertIsInstance(MetadataPathFinder, type)