def test_mockPTYSetUid(self):
        """
        Try creating a PTY process with setting its uid: it's almost the same
        path as the standard path, but with a C{switchUID} call before the
        exec.
        """
        cmd = b'/mock/ouch'

        d = defer.Deferred()
        p = TrivialProcessProtocol(d)
        try:
            reactor.spawnProcess(p, cmd, [b'ouch'], env=None,
                                 usePTY=True, uid=8081)
        except SystemError:
            self.assertTrue(self.mockos.exited)
            self.assertEqual(
                self.mockos.actions,
                [('fork', False), 'setsid', ('setuid', 0), ('setgid', 0),
                 ('switchuid', 8081, 1234), 'exec', ('exit', 1)])
        else:
            self.fail("Should not be here")

        Try creating a PTY process with setting its uid: it's almost the same
        path as the standard path, but with a C{switchUID} call before the
        exec.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/test/test_process.py