tests: add simple test for small consecutive writes

This test was written for: 4d4504486d.

programs/tests/CMakeLists.txt

@@ -1,5 +1,6 @@
 # List of programs.
 set(TEST_LIST
+    t_write_read.c
     t_gid.c
     t_alarm.c
     t_periodic3.c

programs/tests/t_write_read.c

@@ -0,0 +1,58 @@
+/// @file t_write_read.c
+/// @brief Test consecutive writes
+/// @copyright (c) 2024 This file is distributed under the MIT License.
+/// See LICENSE.md for details.
+
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <strerror.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <sys/unistd.h>
+
+int main(int argc, char *argv[])
+{
+    char *file = "t_write_read_file";
+    mode_t mode = S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP;
+
+    int fd = creat(file, mode);
+    if (fd < 0) {
+        printf("Failed to open file %s: %s\n", file, strerror(errno));
+        exit(EXIT_FAILURE);
+    }
+
+    if (write(fd, "foo", 3) != 3) {
+        printf("First write to %s failed: %s\n", file, strerror(errno));
+        exit(1);
+    }
+
+    if (write(fd, "bar", 3) != 3) {
+        printf("Second write to %s failed: %s\n", file, strerror(errno));
+        exit(1);
+    }
+
+    close(fd);
+
+    fd = open(file, O_RDONLY, 0);
+    if (fd < 0) {
+        printf("Failed to open file %s: %s\n", file, strerror(errno));
+        exit(1);
+    }
+
+    ssize_t bytes_read;
+    char buf[7];
+    buf[6] = 0;
+    if ((bytes_read = read(fd, &buf, 6)) < 0) {
+        printf("Reading from file %s failed: %s\n", file, strerror(errno));
+        exit(1);
+    }
+
+    if (strcmp(buf, "foobar") != 0) {
+        printf("Unexpected file content: %s\n", buf);
+        exit(1);
+    }
+
+    unlink(file);
+    return 0;
+}