code: def test_mangle_prefix(self):
      a = PackageMangler()
      mangled = a.mangle("foo.bar")
      mangle_prefix = get_mangle_prefix(mangled)
      self.assertEqual(mangle_prefix + "." + "foo.bar", mangled)
  
file_path: pytorch/test/package/test_mangling.py
imports: from io import BytesIO
  from torch.package import PackageExporter, PackageImporter
  from torch.package._mangling import demangle, get_mangle_prefix, is_mangled, PackageMangler
  from torch.testing._internal.common_utils import run_tests
label_desc: Use image node_id 8 for calling the TestMangling obj's underlying member method code with example usage: obj.test_mangle_prefix() without return types