diff --git a/lib/testing/classes/nasty_strings.php b/lib/testing/classes/nasty_strings.php
new file mode 100644
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+++ b/lib/testing/classes/nasty_strings.php
@@ -0,0 +1,116 @@
+<?php
+// This file is part of Moodle - http://moodle.org/
+//
+// Moodle 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.
+//
+// Moodle 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 Moodle.  If not, see <http://www.gnu.org/licenses/>.
+
+/**
+ * Nasty strings to use in tests.
+ *
+ * @package   core
+ * @category  test
+ * @copyright 2013 David Monllaó
+ * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+
+defined('MOODLE_INTERNAL') || die;
+
+/**
+ * Nasty strings manager.
+ *
+ * Responds to nasty strings requests with a random string of the list
+ * to try with different combinations in different places.
+ *
+ * @package   core
+ * @category  test
+ * @copyright 2013 David Monllaó
+ * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+class nasty_strings {
+
+    /**
+     * List of different strings to fill fields and assert against them
+     *
+     * Non of these strings can be a part of another one, this would not be good
+     * when using more one string at the same time and asserting results.
+     *
+     * @static
+     * @var array
+     */
+    protected static $strings = array(
+        '< > & &lt; &gt; &amp; \' \\" \ \'$@NULL@$ @@TEST@@ \\\" \\ , ; : .   日本語 ­ % %% ',
+        '&amp; \' \\" \ \'$@NULL@$ < > & &lt; &gt; @@TEST@@ \\\" \\ , ; : .   日本語 ­ % %% ',
+        '< > & &lt; &gt; &amp; \' \\" \ \\\" \\ , ; : .   \'$@NULL@$ @@TEST@@ 日本語 ­ % %% ',
+        '< > & &lt; &gt; &amp; \' \\" \ \'$@NULL@$ 日本語 ­ % %%@@TEST@@ \\\" \\ , ; : .    ',
+        '< > & &lt; &gt;  \\\" \\ , ; : .   日本語&amp; \' \\" \ \'$@NULL@$ @@TEST@@ ­ % %% ',
+        '\' \\" \ \'$@NULL@$ @@TEST@@ < > & &lt; &gt; &amp; \\\" \\ , ; : .   日本語 ­ % %% ',
+        '\\\" \\ , ; : .   日本語 ­ % < > & &lt; &gt; &amp; \' \\" \ \'$@NULL@$ @@TEST@@ %% ',
+        '< > & &lt; &gt; &amp; \' \\" \ \'$@NULL@$ 日本語 ­ % %% @@TEST@@ \\\" \\ , ; : .   ',
+        '.   日本語&amp; \' \\"< > & &lt; &gt;  \\\" \\ , ; :  \ \'$@NULL@$ @@TEST@@ ­ % %% ',
+        '&amp; \' \\" \ < > & &lt; &gt;  \\\" \\ , ; : .   日本語\'$@NULL@$ @@TEST@@ ­ % %% ',
+    );
+
+    /**
+     * Already used nasty strings.
+     *
+     * This array will be cleaned before each scenario.
+     *
+     * @static
+     * @var array
+     */
+    protected static $usedstrings = array();
+
+    /**
+     * Returns a nasty string and stores the key mapping.
+     *
+     * @static
+     * @param string $key The key
+     * @return string
+     */
+    public static function get($key) {
+
+        // If have been used during the this tests return it.
+        if (isset(self::$usedstrings[$key])) {
+            return self::$strings[self::$usedstrings[$key]];
+        }
+
+        // Getting non-used random string.
+        do {
+            $index = self::random_index();
+        } while (in_array($index, self::$usedstrings));
+
+        // Mark the string as already used.
+        self::$usedstrings[$key] = $index;
+
+        return self::$strings[$index];
+    }
+
+    /**
+     * Resets the used strings var.
+     * @static
+     * @return void
+     */
+    public static function reset_used_strings() {
+        self::$usedstrings = array();
+    }
+
+    /**
+     * Returns a random index.
+     * @static
+     * @return int
+     */
+    protected static function random_index() {
+        return mt_rand(0, count(self::$strings) - 1);
+    }
+
+}