def test_unicodeSiblingExtension(self):
        """
        C{siblingExtension} called with L{unicode} on a L{unicode}-mode
        L{FilePath} will return a L{unicode}-mode L{FilePath}.
        """
        fp = filepath.FilePath(u"./mon\u20acy")
        sibling = filepath.FilePath(fp._asTextPath() + u".txt")
        sibling.touch()

        newPath = fp.siblingExtension(u".txt")

        self.assertIsInstance(newPath, filepath.FilePath)
        self.assertIsInstance(newPath.path, unicode)

        C{siblingExtension} called with L{unicode} on a L{unicode}-mode
        L{FilePath} will return a L{unicode}-mode L{FilePath}.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/test/test_paths.py