def _spawn(script, outputFD):
    """
    Start a script that is a peer of this test as a subprocess.

    @param script: the module name of the script in this directory (no
        package prefix, no '.py')
    @type script: C{str}

    @rtype: L{StartStopProcessProtocol}
    """
    pyExe = FilePath(sys.executable).asBytesMode().path
    env = bytesEnviron()
    env[b"PYTHONPATH"] = FilePath(
        pathsep.join(sys.path)).asBytesMode().path
    sspp = StartStopProcessProtocol()
    reactor.spawnProcess(
        sspp, pyExe, [
            pyExe,
            FilePath(__file__).sibling(script + ".py").asBytesMode().path,
            intToBytes(outputFD),
        ],
        env=env,
        childFDs={0: "w", 1: "r", 2: "r", outputFD: outputFD}
    )
    return sspp

    Start a script that is a peer of this test as a subprocess.

    @param script: the module name of the script in this directory (no
        package prefix, no '.py')
    @type script: C{str}

    @rtype: L{StartStopProcessProtocol}
    
stackoverflow/venv/lib/python3.6/site-packages/twisted/python/test/test_sendmsg.py