ptsname
char *ptsname(int);
child = child_spawn(ptsname(pty));
REQUIRE_LIBC(pts = ptsname(hostfd), NULL);
REQUIRE_LIBC(pts = ptsname(hostfd), NULL);
REQUIRE_ERRNO((pty = ptsname(fdm)), NULL);
REQUIRE_LIBC(pts = ptsname(hostfd), NULL);