def test_errorTab(self):
        """
        L{_ErrorFormatter.formatError} should use C{errorTab} if it is supplied
        and contains the requested error code.
        """
        formatter = _ErrorFormatter(
            None, None, {self.probeErrorCode: self.probeMessage})
        message = formatter.formatError(self.probeErrorCode)
        self.assertEqual(message, self.probeMessage)

        L{_ErrorFormatter.formatError} should use C{errorTab} if it is supplied
        and contains the requested error code.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/test/test_strerror.py