def test_customExtension(self):
        """
        L{FilePath.setContent} creates temporary files with a user-supplied
        extension so that if it is somehow interrupted while writing them the
        file that it leaves behind will be identifiable.
        """
        fp = TrackingFilePath(self.mktemp())
        fp.setContent(b"goodbye", b"-something-else")
        self._assertOneOpened(fp, b"-something-else")

        L{FilePath.setContent} creates temporary files with a user-supplied
        extension so that if it is somehow interrupted while writing them the
        file that it leaves behind will be identifiable.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/test/test_paths.py