Test for correct posix_spawn behavior when pgrp = 0

spawntest.c

#include <errno.h>
#include <signal.h>
#include <spawn.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

#define nullptr 0

int main(int argc, const char *argv[]) {
	posix_spawnattr_t attr;
	posix_spawnattr_init(&attr);
	uint8_t flags = 0;

	flags |= POSIX_SPAWN_SETPGROUP;
	posix_spawnattr_setpgroup(&attr, 0);

	posix_spawnattr_setflags(&attr, flags);

	posix_spawn_file_actions_t actions;
	posix_spawn_file_actions_init(&actions);
	posix_spawn_file_actions_adddup2(&actions, STDIN_FILENO, STDIN_FILENO);
	posix_spawn_file_actions_adddup2(&actions, STDOUT_FILENO, STDOUT_FILENO);
	posix_spawn_file_actions_adddup2(&actions, STDERR_FILENO, STDERR_FILENO);

	const char * new_argv[] = {
		"/bin/cat",
		nullptr
	};

	const char * envp[] = {
		nullptr
	};

	pid_t child_pid = 0;

	int result = posix_spawn(&child_pid, "/bin/cat", &actions, &attr, (char *const *) new_argv, (char *const *) envp);

	if (result != 0) {
		fprintf(stderr, "posix_spawn(\"/bin/cat\") failed! errno: %d\n", errno);
		return errno;
	}

	pid_t child_pgrp = getpgid(child_pid);

	pid_t own_pid = getpid();
	pid_t own_pgrp = getpgrp();

	printf("own pid: %d\n", own_pid);
	printf("own pgid: %d\n\n", own_pgrp);

	printf("child pid: %d\n", child_pid);
	printf("child pgid: %d\n\n", child_pgrp);

	kill(child_pid, SIGKILL);

	if (child_pgrp != child_pid) {
		fprintf(stderr, "Test failed: child_pgid != child_pid though `posix_spawnattr_setpgroup(&attr, 0)` was specified!\n");
		return -1;
	}

	printf("Test passed.\n");

	return 0;
}