def setUp(self):
        """
        Get the text from --help-reactors
        """
        self.options = app.ReactorSelectionMixin()
        self.options.messageOutput = NativeStringIO()
        self.assertRaises(SystemExit, self.options.opt_help_reactors)
        self.message = self.options.messageOutput.getvalue()

        Get the text from --help-reactors
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/test/test_application.py