def test_value(self):
        """
        The L{Deferred} returned by L{getProcessValue} is fired with the exit
        status of the child process.
        """
        scriptFile = self.makeSourceFile(["raise SystemExit(1)"])

        d = utils.getProcessValue(self.exe, ['-u', scriptFile])
        return d.addCallback(self.assertEqual, 1)

        The L{Deferred} returned by L{getProcessValue} is fired with the exit
        status of the child process.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/test/test_iutils.py