--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,10 @@
 2011-09-20  Bruno Haible  <bruno@clisp.org>
 
+	Tests for module 'ftruncate'.
+	* modules/ftruncate-tests: New file.
+	* tests/test-ftruncate.sh: New file.
+	* tests/test-ftruncate.c: New file.
+
 	fsync tests: EBADF tests.
 	* tests/test-fsync.c (main): Add more tests for EBADF.
 

new file mode 100644
--- /dev/null
+++ b/modules/ftruncate-tests
@@ -0,0 +1,13 @@
+Files:
+tests/test-ftruncate.c
+tests/test-ftruncate.sh
+tests/signature.h
+tests/macros.h
+
+Depends-on:
+
+configure.ac:
+
+Makefile.am:
+TESTS += test-ftruncate.sh
+check_PROGRAMS += test-ftruncate

new file mode 100644
--- /dev/null
+++ b/tests/test-ftruncate.c
@@ -0,0 +1,57 @@
+/* Test truncating a file.
+   Copyright (C) 2011 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/>.  */
+
+#include <config.h>
+
+#include <unistd.h>
+
+#include "signature.h"
+SIGNATURE_CHECK (ftruncate, int, (int, off_t));
+
+#include <errno.h>
+#include <fcntl.h>
+
+#include "macros.h"
+
+int
+main (int argc, char *argv[])
+{
+  const char *filename = argv[1];
+
+  /* Test behaviour for invalid file descriptors.  */
+  {
+    errno = 0;
+    ASSERT (ftruncate (-1, 0) == -1);
+    ASSERT (errno == EBADF);
+  }
+  {
+    errno = 0;
+    ASSERT (ftruncate (99, 0) == -1);
+    ASSERT (errno == EBADF);
+  }
+
+  /* Test behaviour for read-only file descriptors.  */
+  {
+    int fd = open (filename, O_RDONLY);
+    ASSERT (fd >= 0);
+    errno = 0;
+    ASSERT (ftruncate (fd, 0) == -1);
+    ASSERT (errno == EBADF || errno == EINVAL);
+    close (fd);
+  }
+
+  return 0;
+}

new file mode 100755
--- /dev/null
+++ b/tests/test-ftruncate.sh
@@ -0,0 +1,3 @@
+#!/bin/sh
+
+exec ./test-ftruncate${EXEEXT} "$srcdir/test-ftruncate.sh"