def _spawnProcess(self, proto, sibling, *args, **kw):
        """
        Launch a child Python process and communicate with it using the
        given ProcessProtocol.

        @param proto: A L{ProcessProtocol} instance which will be connected
        to the child process.

        @param sibling: The basename of a file containing the Python program
        to run in the child process.

        @param *args: strings which will be passed to the child process on
        the command line as C{argv[2:]}.

        @param **kw: additional arguments to pass to L{reactor.spawnProcess}.

        @return: The L{IProcessTransport} provider for the spawned process.
        """
        args = [sys.executable,
                b"-m", b"twisted.test." + sibling,
                reactor.__class__.__module__] + list(args)
        return reactor.spawnProcess(
            proto,
            sys.executable,
            args,
            env=properEnv,
            **kw)

        Launch a child Python process and communicate with it using the
        given ProcessProtocol.

        @param proto: A L{ProcessProtocol} instance which will be connected
        to the child process.

        @param sibling: The basename of a file containing the Python program
        to run in the child process.

        @param *args: strings which will be passed to the child process on
        the command line as C{argv[2:]}.

        @param **kw: additional arguments to pass to L{reactor.spawnProcess}.

        @return: The L{IProcessTransport} provider for the spawned process.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/test/test_stdio.py