Implement dprintf and vdprintf

tests/stdio/dprintf.c

@@ -0,0 +1,24 @@
+#include <stdio.h>
+#include <fcntl.h>
+
+#include "test_helpers.h"
+
+int main(void)
+{
+    int fd = open("/dev/stdout", O_WRONLY, 0222);
+    ERROR_IF(open, fd, < 0);
+
+    const char *msg = "Hello, %s";
+
+    int result = dprintf(fd, msg, "world");
+    ERROR_IF(dprintf, result, != sizeof("Hello, world") - 1);
+    UNEXP_IF(dprintf, result, < 0);
+
+    result = dprintf(fd, "\na\n");
+    UNEXP_IF(dprintf, result, < 0);
+    ERROR_IF(dprintf, result, != sizeof("\na\n") - 1);
+
+    close(fd);
+
+    return 0;
+}