def test_testmoduleTwice(self):
        """
        When the same module is specified with two --testmodule flags, it
        should only appear once in the suite.
        """
        self.config.opt_testmodule(sibpath('moduletest.py'))
        self.config.opt_testmodule(sibpath('moduletest.py'))
        self.assertSuitesEqual(trial._getSuite(self.config),
                               ['twisted.trial.test.test_log'])

        When the same module is specified with two --testmodule flags, it
        should only appear once in the suite.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/trial/test/test_script.py