def test_frameElementLineNumber(self):
        """
        The I{lineNumber} renderer of L{_FrameElement} renders the line number
        associated with the frame object used to initialize the
        L{_FrameElement}.
        """
        element = _FrameElement(
            TagLoader(tags.span(render="lineNumber")),
            self.frame)
        d = flattenString(None, element)
        d.addCallback(
            self.assertEqual, b"<span>" + intToBytes(self.base + 1) + b"</span>")
        return d

        The I{lineNumber} renderer of L{_FrameElement} renders the line number
        associated with the frame object used to initialize the
        L{_FrameElement}.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/web/test/test_util.py