gh-154690: Test ensure_distinct_paths() fallback when resolve() fails

Cover AttributeError and OSError from resolve(), which fall back to the
lexical self-copy check.

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: dura0ok

Lib/test/test_pathlib/test_pathlib.py

@@ -1481,6 +1481,17 @@ def test_copy_dir_into_itself_via_symlink(self):
         self.assertRaises(OSError, source.copy, target, follow_symlinks=False)
         self.assertFalse((source / 'copyC').exists())
 
+    def test_copy_dir_into_itself_when_resolve_fails(self):
+        # Fall back to lexical comparison if resolve() is missing or errors.
+        base = self.cls(self.base)
+        source = base / 'dirC'
+        target = source / 'copyC'
+        for exc in (AttributeError, OSError):
+            with self.subTest(exc=exc):
+                with mock.patch.object(self.cls, 'resolve', side_effect=exc):
+                    self.assertRaises(OSError, source.copy, target)
+                    self.assertFalse(target.exists())
+
     @needs_symlinks
     def test_copy_directory_symlink_to_existing_symlink(self):
         base = self.cls(self.base)