public function for_html_attr_test()
 {
     $safe_string = new SafeString('"<em>Foo</em>\'s bar"');
     $attr_string = $safe_string->for_html_attr();
     $this->assert_equal('&quot;&lt;em&gt;Foo&lt;/em&gt;&#039;s bar&quot;', $attr_string);
 }