def test_daemonizedNoUmask(self):
        """
        L{UnixApplicationRunner.setupEnvironment} changes the process umask to
        C{0077} if L{None} is passed for the C{umask} parameter and C{False} is
        passed for the C{nodaemon} parameter.
        """
        with AlternateReactor(FakeDaemonizingReactor()):
            self.runner.setupEnvironment(None, ".", False, None, None)
        self.assertEqual(self.mask, 0o077)

        L{UnixApplicationRunner.setupEnvironment} changes the process umask to
        C{0077} if L{None} is passed for the C{umask} parameter and C{False} is
        passed for the C{nodaemon} parameter.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/test/test_twistd.py