--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,9 @@
 2009-10-18  Bruno Haible  <bruno@clisp.org>
 
+	Tests for module 'isblank'.
+	* modules/isblank-tests: New file.
+	* tests/test-isblank.c: New file.
+
 	New module 'isblank'.
 	* lib/isblank.c: New file.
 	* m4/isblank.m4: New file.

new file mode 100644
--- /dev/null
+++ b/modules/isblank-tests
@@ -0,0 +1,10 @@
+Files:
+tests/test-isblank.c
+
+Depends-on:
+
+configure.ac:
+
+Makefile.am:
+TESTS += test-isblank
+check_PROGRAMS += test-isblank

new file mode 100644
--- /dev/null
+++ b/tests/test-isblank.c
@@ -0,0 +1,58 @@
+/* Test of isblank() function.
+   Copyright (C) 2009 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>, 2009.  */
+
+#include <config.h>
+
+#include <ctype.h>
+
+#include <limits.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#define ASSERT(expr) \
+  do									     \
+    {									     \
+      if (!(expr))							     \
+        {								     \
+          fprintf (stderr, "%s:%d: assertion failed\n", __FILE__, __LINE__); \
+          fflush (stderr);						     \
+          abort ();							     \
+        }								     \
+    }									     \
+  while (0)
+
+int
+main (int argc, char *argv[])
+{
+  unsigned int c;
+
+  /* Verify the property in the "C" locale.
+     POSIX specifies in
+       <http://www.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap07.html>
+     that
+       - in all locales, the blank characters include the <space> and <tab>
+         characters,
+       - in the "POSIX" locale (which is usually the same as the "C" locale),
+         the blank characters include only the ASCII <space> and <tab>
+         characters.  */
+  for (c = 0; c <= UCHAR_MAX; c++)
+    ASSERT (!isblank (c) == !(c == ' ' || c == '\t'));
+  ASSERT (!isblank (EOF));
+
+  return 0;
+}