new file mode 100644
--- /dev/null
+++ b/modules/strcasestr-tests
@@ -0,0 +1,11 @@
+Files:
+tests/test-strcasestr.c
+
+Depends-on:
+
+configure.ac:
+
+Makefile.am:
+TESTS += test-strcasestr
+check_PROGRAMS += test-strcasestr
+

new file mode 100644
--- /dev/null
+++ b/tests/test-strcasestr.c
@@ -0,0 +1,134 @@
+/* Test of case-insensitive searching in a string.
+   Copyright (C) 2007 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 2, 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, write to the Free Software Foundation,
+   Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
+
+/* Written by Bruno Haible <bruno@clisp.org>, 2007.  */
+
+#ifdef HAVE_CONFIG_H
+# include <config.h>
+#endif
+
+#include <string.h>
+
+#include <stdlib.h>
+
+#define ASSERT(expr) if (!(expr)) abort ();
+
+int
+main ()
+{
+  {
+    const char input[] = "foo";
+    const char *result = strcasestr (input, "");
+    ASSERT (result == input);
+  }
+
+  {
+    const char input[] = "foo";
+    const char *result = strcasestr (input, "O");
+    ASSERT (result == input + 1);
+  }
+
+  {
+    const char input[] = "ABC ABCDAB ABCDABCDABDE";
+    const char *result = strcasestr (input, "ABCDaBD");
+    ASSERT (result == input + 15);
+  }
+
+  {
+    const char input[] = "ABC ABCDAB ABCDABCDABDE";
+    const char *result = strcasestr (input, "ABCDaBE");
+    ASSERT (result == NULL);
+  }
+
+  /* Check that a very long haystack is handled quickly if the needle is
+     short and occurs near the beginning.  */
+  {
+    size_t repeat = 10000;
+    size_t m = 1000000;
+    char *needle =
+      "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA"
+      "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaAaaaaaaAAAAaaaaaaa"
+      "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA";
+    char *haystack = (char *) malloc (m + 1);
+    if (haystack != NULL)
+      {
+	memset (haystack, 'A', m);
+	haystack[0] = 'B';
+	haystack[m] = '\0';
+
+	for (; repeat > 0; repeat--)
+	  {
+	    ASSERT (strcasestr (haystack, needle) == haystack + 1);
+	  }
+
+	free (haystack);
+      }
+  }
+
+  /* Check that a very long needle is discarded quickly if the haystack is
+     short.  */
+  {
+    size_t repeat = 10000;
+    size_t m = 1000000;
+    char *haystack =
+      "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA"
+      "ABABABABABABABABABABABABABABABABABABABABABABABABABABABABABABABABABAB";
+    char *needle = (char *) malloc (m + 1);
+    if (needle != NULL)
+      {
+	memset (needle, 'A', m);
+	needle[m] = '\0';
+
+	for (; repeat > 0; repeat--)
+	  {
+	    ASSERT (strcasestr (haystack, needle) == NULL);
+	  }
+
+	free (needle);
+      }
+  }
+
+  /* Check that the asymptotic worst-case complexity is not quadratic.  */
+#if !HAVE_STRCASESTR /* The system's strcasestr() function fails this test.  */
+  {
+    size_t m = 1000000;
+    char *haystack = (char *) malloc (2 * m + 2);
+    char *needle = (char *) malloc (m + 2);
+    if (haystack != NULL && needle != NULL)
+      {
+	const char *result;
+
+	memset (haystack, 'A', 2 * m);
+	haystack[2 * m] = 'B';
+	haystack[2 * m + 1] = '\0';
+
+	memset (needle, 'a', m);
+	needle[m] = 'B';
+	needle[m + 1] = '\0';
+
+	result = strcasestr (haystack, needle);
+	ASSERT (result == haystack + m);
+      }
+    if (needle != NULL)
+      free (needle);
+    if (haystack != NULL)
+      free (haystack);
+  }
+#endif
+
+  return 0;
+}