def test_uninstallHandler(self):
        """
        C{installHandler(-1)} removes the SIGCHLD handler completely.
        """
        read, write = self.pipe()
        self.assertTrue(isDefaultHandler())
        installHandler(write)
        self.assertFalse(isDefaultHandler())
        installHandler(-1)
        self.assertTrue(isDefaultHandler())

        C{installHandler(-1)} removes the SIGCHLD handler completely.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/internet/test/test_sigchld.py