This functionality is tested in tests/fs/vfs/t_io

regress/sys/kern/write_append/Makefile

@@ -1,15 +0,0 @@
-#	$NetBSD: Makefile,v 1.1 2008/08/27 06:40:13 christos Exp $
-
-NOMAN=		# defined
-
-PROG=		write_append
-WARNS?=		4
-
-regress:
-	@if ${.OBJDIR}/${PROG} 2> /dev/null; then \
-		echo "PASSED"; \
-	else \
-		echo "FAILED"; \
-	fi
-
-.include <bsd.prog.mk>

regress/sys/kern/write_append/write_append.c

@@ -1,34 +0,0 @@
-#include <err.h>
-#include <unistd.h>
-#include <fcntl.h>
-
-static const char fn[] = "/tmp/write-test.txt";
-static const char str[] = "Test write() append\n";
-static size_t len = sizeof(str) - 1;
-
-int
-main(void)
-{
-	int fd;
-	off_t off;
-
-	if ((fd = open(fn, O_CREAT | O_RDWR, 0600)) == -1)
-		err(1, "Cannot open `%s'", fn);
-	if (write(fd, str, len) != (ssize_t)len)
-		err(1, "Write failed");
-	if (close(fd) == -1)
-		err(1, "Close failed");
-	if ((fd = open(fn, O_WRONLY | O_APPEND)) == -1)
-		err(1, "Cannot open `%s'", fn);
-        if ((off = lseek(fd, (off_t) 0, SEEK_SET)) != (off_t)0)
-		err(1, "Seek failed");
-	if (write(fd, str, 0) != 0)
-		err(1, "Write failed");
-        if ((off = lseek(fd, (off_t) 0, SEEK_CUR)) != (off_t)0)
-		errx(1, "bad seek offset %lld\n", (long long)off);
-	if (close(fd) == -1)
-		err(1, "Close failed");
-	if (unlink(fn) == -1)
-		err(1, "Unlink failed");
-	return 0;
-}