--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,9 @@
 2010-01-09  Bruno Haible  <bruno@clisp.org>
 
+	Tests for module 'unistr/u8-mblen'.
+	* modules/unistr/u8-mblen-tests: New file.
+	* tests/unistr/test-u8-mblen.c: New file.
+
 	Tests for module 'unistr/u32-to-u16'.
 	* modules/unistr/u32-to-u16-tests: New file.
 	* tests/unistr/test-u32-to-u16.c: New file.

new file mode 100644
--- /dev/null
+++ b/modules/unistr/u8-mblen-tests
@@ -0,0 +1,12 @@
+Files:
+tests/unistr/test-u8-mblen.c
+tests/macros.h
+
+Depends-on:
+
+configure.ac:
+
+Makefile.am:
+TESTS += test-u8-mblen
+check_PROGRAMS += test-u8-mblen
+test_u8_mblen_SOURCES = unistr/test-u8-mblen.c

new file mode 100644
--- /dev/null
+++ b/tests/unistr/test-u8-mblen.c
@@ -0,0 +1,155 @@
+/* Test of u8_mblen() 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 "macros.h"
+
+int
+main ()
+{
+  int ret;
+
+  /* Test zero-length input.  */
+  {
+    static const uint8_t input[] = "";
+    ret = u8_mblen (input, 0);
+    ASSERT (ret == -1);
+  }
+
+  /* Test NUL unit input.  */
+  {
+    static const uint8_t input[] = "";
+    ret = u8_mblen (input, 1);
+    ASSERT (ret == 0);
+  }
+
+  /* Test ISO 646 unit input.  */
+  {
+    ucs4_t c;
+    uint8_t buf[1];
+
+    for (c = 1; c < 0x80; c++)
+      {
+        buf[0] = c;
+        ret = u8_mblen (buf, 1);
+        ASSERT (ret == 1);
+      }
+  }
+
+  /* Test 2-byte character input.  */
+  {
+    static const uint8_t input[] = { 0xC3, 0x97 };
+    ret = u8_mblen (input, 2);
+    ASSERT (ret == 2);
+  }
+
+  /* Test 3-byte character input.  */
+  {
+    static const uint8_t input[] = { 0xE2, 0x82, 0xAC };
+    ret = u8_mblen (input, 3);
+    ASSERT (ret == 3);
+  }
+
+  /* Test 4-byte character input.  */
+  {
+    static const uint8_t input[] = { 0xF4, 0x8F, 0xBF, 0xBD };
+    ret = u8_mblen (input, 4);
+    ASSERT (ret == 4);
+  }
+
+  /* Test incomplete/invalid 1-byte input.  */
+  {
+    static const uint8_t input[] = { 0xC1 };
+    ret = u8_mblen (input, 1);
+    ASSERT (ret == -1);
+  }
+  {
+    static const uint8_t input[] = { 0xC3 };
+    ret = u8_mblen (input, 1);
+    ASSERT (ret == -1);
+  }
+  {
+    static const uint8_t input[] = { 0xE2 };
+    ret = u8_mblen (input, 1);
+    ASSERT (ret == -1);
+  }
+  {
+    static const uint8_t input[] = { 0xF4 };
+    ret = u8_mblen (input, 1);
+    ASSERT (ret == -1);
+  }
+  {
+    static const uint8_t input[] = { 0xFE };
+    ret = u8_mblen (input, 1);
+    ASSERT (ret == -1);
+  }
+
+  /* Test incomplete/invalid 2-byte input.  */
+  {
+    static const uint8_t input[] = { 0xE0, 0x9F };
+    ret = u8_mblen (input, 2);
+    ASSERT (ret == -1);
+  }
+  {
+    static const uint8_t input[] = { 0xE2, 0x82 };
+    ret = u8_mblen (input, 2);
+    ASSERT (ret == -1);
+  }
+  {
+    static const uint8_t input[] = { 0xE2, 0xD0 };
+    ret = u8_mblen (input, 2);
+    ASSERT (ret == -1);
+  }
+  {
+    static const uint8_t input[] = { 0xF0, 0x8F };
+    ret = u8_mblen (input, 2);
+    ASSERT (ret == -1);
+  }
+  {
+    static const uint8_t input[] = { 0xF3, 0x8F };
+    ret = u8_mblen (input, 2);
+    ASSERT (ret == -1);
+  }
+  {
+    static const uint8_t input[] = { 0xF3, 0xD0 };
+    ret = u8_mblen (input, 2);
+    ASSERT (ret == -1);
+  }
+
+  /* Test incomplete/invalid 3-byte input.  */
+  {
+    static const uint8_t input[] = { 0xF3, 0x8F, 0xBF };
+    ret = u8_mblen (input, 3);
+    ASSERT (ret == -1);
+  }
+  {
+    static const uint8_t input[] = { 0xF3, 0xD0, 0xBF };
+    ret = u8_mblen (input, 3);
+    ASSERT (ret == -1);
+  }
+  {
+    static const uint8_t input[] = { 0xF3, 0x8F, 0xD0 };
+    ret = u8_mblen (input, 3);
+    ASSERT (ret == -1);
+  }
+
+  return 0;
+}