def test_temporarySiblingExtension(self):
        """
        If L{FilePath.temporarySibling} is given an extension argument, it will
        produce path objects with that extension appended to their names.
        """
        testExtension = b".test-extension"
        ts = self.path.temporarySibling(testExtension)
        self.assertTrue(ts.basename().endswith(testExtension),
                        "%s does not end with %s" % (
                            ts.basename(), testExtension))

        If L{FilePath.temporarySibling} is given an extension argument, it will
        produce path objects with that extension appended to their names.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/test/test_paths.py