def test_isDefaultHandler(self):
        """
        L{isDefaultHandler} returns true if the SIGCHLD handler is SIG_DFL,
        false otherwise.
        """
        self.assertTrue(isDefaultHandler())
        signal.signal(signal.SIGCHLD, signal.SIG_IGN)
        self.assertFalse(isDefaultHandler())
        signal.signal(signal.SIGCHLD, signal.SIG_DFL)
        self.assertTrue(isDefaultHandler())
        signal.signal(signal.SIGCHLD, lambda *args: None)
        self.assertFalse(isDefaultHandler())

        L{isDefaultHandler} returns true if the SIGCHLD handler is SIG_DFL,
        false otherwise.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/internet/test/test_sigchld.py