Begin

[tl-append] / tl-append-test.c

#define _POSIX_C_SOURCE 2
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

static void die(const char *message) {
  fputs(message, stderr);
  fputc('\n', stderr);
  exit(1);
}

static void die_err(const char *message) {
  perror(message);
  exit(1);
}

static void write_and_read_line() {
  char buf[10];

  FILE *p = popen("./tl-append", "w");
  if (p == NULL)
    die_err("Couldn't run tl-append");
  if (fputs("foo\n", p) == EOF)
    die("Couldn't write to pipe");
  int status = pclose(p);
  if (status < 0)
    die_err("Error closing pipe");
  if (status != 0)
    die("tl-append exited abnormally");

  FILE *f = fopen("tl.log", "r");
  if (f == NULL)
    die_err("Error opening log file");
  if (fgets(buf, sizeof(buf), f) == NULL)
    die("Error reading log file");
  if (strncmp("foo\n", buf, sizeof(buf)) != 0)
    die("Wrong contents in log file");
  if (fclose(f) != 0)
    die_err("Error closing log file");
}

int main() { write_and_read_line(); }