def assertDeprecationWarningOf(method):
            """
            Check that a deprecation warning is present.
            """
            warningsShown = self.flushWarnings([self.test_deprecation])
            self.assertEqual(len(warningsShown), 1)
            self.assertIdentical(
                warningsShown[0]['category'], DeprecationWarning)
            self.assertEqual(
                warningsShown[0]['message'],
                'twisted.web.html.%s was deprecated in Twisted 15.3.0; '
                'please use twisted.web.template instead' % (
                    method,),
                )

            Check that a deprecation warning is present.
            
stackoverflow/venv/lib/python3.6/site-packages/twisted/web/test/test_html.py