def test_stdin(self):
        """
        Making sure getPassword accepts a password from standard input by
        running a child process which uses getPassword to read in a string
        which it then writes it out again.  Write a string to the child
        process and then read one and make sure it is the right string.
        """
        p = PasswordTestingProcessProtocol()
        p.finished = Deferred()
        reactor.spawnProcess(
            p, pyExe,
            [pyExe,
             b'-c',
             (b'import sys\n'
              b'from twisted.python.util import getPassword\n'
              b'sys.stdout.write(getPassword())\n'
              b'sys.stdout.flush()\n')],
            env={b'PYTHONPATH': os.pathsep.join(sys.path).encode("utf8")})

        def processFinished(result):
            (reason, output) = result
            reason.trap(ProcessDone)
            self.assertIn((1, b'secret'), output)

        return p.finished.addCallback(processFinished)

        Making sure getPassword accepts a password from standard input by
        running a child process which uses getPassword to read in a string
        which it then writes it out again.  Write a string to the child
        process and then read one and make sure it is the right string.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/python/test/test_util.py