def setUp(self):
        """
        Clear the SIGCHLD handler, if there is one, to ensure an environment
        like the one which exists prior to a call to L{reactor.run}.
        """
        if not platform.isWindows():
            self.originalHandler = signal.signal(signal.SIGCHLD, signal.SIG_DFL)

        Clear the SIGCHLD handler, if there is one, to ensure an environment
        like the one which exists prior to a call to L{reactor.run}.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/internet/test/reactormixins.py