def METHOD_NAME(self):
    build_appliance_pair = (__package__, "build-appliance")
    with tempfile.TemporaryFile(
        mode="w+b"
    ) as curl_stdout, tempfile.TemporaryDirectory() as tmpdir:
        self._nspawn_in(
            build_appliance_pair,
            [
                "--user=root",
                "--run-proxy-server",
                f"--forward-fd={curl_stdout.fileno()}",
                "--",
                "/bin/sh",
                "-c",
                "curl -X GET -I http://localhost:45063/blah -m 3 2>/dev/null \
                | head -1 > /proc/self/fd/3",
            ],
        )
        curl_stdout.seek(0)
        self.assertEqual(
            curl_stdout.readline().strip(),
            b"HTTP/1.0 404 Unknown route: blah",
        )