test: reproduce copyfile() off by one regression

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

test/copyfile.c

@@ -2,16 +2,39 @@
 #include <errno.h>
 #include "check.h"
 
+static int sz()
+{
+	struct stat st;
+	ssize_t len;
+
+	printf("=>Start copyfile(/dev/zero, 32768)\n");
+	len = copyfile("/dev/zero", "/tmp/zeroes", 32768, 0);
+	if (!len)
+		err(1, "failed copying any bytes from /dev/zero");
+
+	if (stat("/tmp/zeroes", &st))
+		err(1, "copied but cannot find destination");
+	if (st.st_size != 32768)
+		err(1, "file only %ld bytes, expected 32768", st.st_size);
+
+	if (len != st.st_size)
+		errx(1, "copied correct num bytes, 32768, but copyfile() returns %ld", len);
+
+	printf("OK => %ld\n", len);
+
+	return 0;
+}
+
 int main(void)
 {
-	int i = 0;
 	char *files[] = {
 		"/etc/passwd", "/tmp/mypwd", "/tmp/mypwd",
-		"/etc/passwd", "/tmp/", "/tmp/passwd",
+		"/etc/passwd", "/tmp/",      "/tmp/passwd",
-		"/etc/passwd", "/tmp", "/tmp/passwd",
+		"/etc/passwd", "/tmp",       "/tmp/passwd",
 		NULL
 	};
 	FILE *src, *dst;
+	int i = 0;
 
 	printf("=>Start testing fcopyfile()\n");
 	while (files[i]) {
@@ -51,5 +74,5 @@ int main(void)
 		i += 3;
 	}
 
-	return 0;
+	return sz();
 }