--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,10 @@
 2010-01-10  Bruno Haible  <bruno@clisp.org>
 
+	Tests for module 'unistr/u8-strncat'.
+	* modules/unistr/u8-strncat-tests: New file.
+	* tests/unistr/test-u8-strncat.c: New file.
+	* tests/unistr/test-strncat.h: New file.
+
 	Tests for module 'unistr/u32-strcat'.
 	* modules/unistr/u32-strcat-tests: New file.
 	* tests/unistr/test-u32-strcat.c: New file.

new file mode 100644
--- /dev/null
+++ b/modules/unistr/u8-strncat-tests
@@ -0,0 +1,20 @@
+Files:
+tests/unistr/test-u8-strncat.c
+tests/unistr/test-strncat.h
+tests/zerosize-ptr.h
+tests/macros.h
+m4/mmap-anon.m4
+
+Depends-on:
+extensions
+getpagesize
+
+configure.ac:
+gl_FUNC_MMAP_ANON
+AC_CHECK_HEADERS_ONCE([sys/mman.h])
+AC_CHECK_FUNCS_ONCE([mprotect])
+
+Makefile.am:
+TESTS += test-u8-strncat
+check_PROGRAMS += test-u8-strncat
+test_u8_strncat_SOURCES = unistr/test-u8-strncat.c

new file mode 100644
--- /dev/null
+++ b/tests/unistr/test-strncat.h
@@ -0,0 +1,90 @@
+/* Test of uN_strncat() functions.
+   Copyright (C) 2010 Free Software Foundation, Inc.
+
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+/* Written by Bruno Haible <bruno@clisp.org>, 2010.  */
+
+static void
+check_single (const UNIT *input, size_t length, size_t n)
+{
+  static const UNIT base[] = { 'C', 'h', 'a', 'n', 'g', 'i', 'n', 'g', 0 };
+  size_t m;
+
+  for (m = 0; m < SIZEOF (base); m++)
+    {
+      UNIT *dest;
+      UNIT *result;
+      size_t i;
+
+      dest = (UNIT *) malloc ((1 + m + n + 2) * sizeof (UNIT));
+      ASSERT (dest != NULL);
+
+      dest[0] = MAGIC;
+      for (i = 0; i < m; i++)
+        dest[1 + i] = base[i];
+      dest[1 + m] = 0;
+      for (i = 1; i < n + 2; i++)
+        dest[1 + m + i] = MAGIC;
+
+      result = U_STRNCAT (dest + 1, input, n);
+      ASSERT (result == dest + 1);
+
+      ASSERT (dest[0] == MAGIC);
+      for (i = 0; i < m; i++)
+        ASSERT (dest[1 + i] == base[i]);
+      for (i = 0; i < (n <= length ? n : length); i++)
+        ASSERT (dest[1 + m + i] == input[i]);
+      ASSERT (dest[1 + m + i] == 0);
+      ASSERT (dest[1 + m + i + 1] == MAGIC);
+
+      free (dest);
+    }
+}
+
+static void
+check (const UNIT *input, size_t input_length)
+{
+  size_t length;
+  size_t n;
+
+  ASSERT (input_length > 0);
+  ASSERT (input[input_length - 1] == 0);
+  length = input_length - 1; /* = U_STRLEN (input) */
+
+  for (n = 0; n <= 2 * length + 2; n++)
+    check_single (input, length, n);
+
+  /* Check that U_STRNCAT (D, S, N) does not look at more than
+     MIN (U_STRLEN (S) + 1, N) units.  */
+  {
+    char *page_boundary = (char *) zerosize_ptr ();
+
+    if (page_boundary != NULL)
+      {
+        for (n = 0; n <= 2 * length + 2; n++)
+          {
+            size_t n_to_copy = (n <= length ? n : length + 1);
+            UNIT *copy;
+            size_t i;
+
+            copy = (UNIT *) page_boundary - n_to_copy;
+            for (i = 0; i < n_to_copy; i++)
+              copy[i] = input[i];
+
+            check_single (copy, length, n);
+          }
+      }
+  }
+}

new file mode 100644
--- /dev/null
+++ b/tests/unistr/test-u8-strncat.c
@@ -0,0 +1,52 @@
+/* Test of u8_strncat() function.
+   Copyright (C) 2010 Free Software Foundation, Inc.
+
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+/* Written by Bruno Haible <bruno@clisp.org>, 2010.  */
+
+#include <config.h>
+
+#include "unistr.h"
+
+#include <stdlib.h>
+
+#include "zerosize-ptr.h"
+#include "macros.h"
+
+#define UNIT uint8_t
+#define U_STRNCAT u8_strncat
+#define MAGIC 0xBA
+#include "test-strncat.h"
+
+int
+main ()
+{
+  /* Simple string.  */
+  { /* "Grüß Gott. Здравствуйте! x=(-b±sqrt(b²-4ac))/(2a)  日本語,中文,한글" */
+    static const uint8_t input[] =
+      { 'G', 'r', 0xC3, 0xBC, 0xC3, 0x9F, ' ', 'G', 'o', 't', 't', '.', ' ',
+        0xD0, 0x97, 0xD0, 0xB4, 0xD1, 0x80, 0xD0, 0xB0, 0xD0, 0xB2, 0xD1, 0x81,
+        0xD1, 0x82, 0xD0, 0xB2, 0xD1, 0x83, 0xD0, 0xB9, 0xD1, 0x82, 0xD0, 0xB5,
+        '!', ' ', 'x', '=', '(', '-', 'b', 0xC2, 0xB1, 's', 'q', 'r', 't', '(',
+        'b', 0xC2, 0xB2, '-', '4', 'a', 'c', ')', ')', '/', '(', '2', 'a', ')',
+        ' ', ' ', 0xE6, 0x97, 0xA5, 0xE6, 0x9C, 0xAC, 0xE8, 0xAA, 0x9E, ',',
+        0xE4, 0xB8, 0xAD, 0xE6, 0x96, 0x87, ',',
+        0xED, 0x95, 0x9C, 0xEA, 0xB8, 0x80, '\0'
+      };
+    check (input, SIZEOF (input));
+  }
+
+  return 0;
+}