Fix a filter_uri() test
diff --git a/tests/codeigniter/core/URI_test.php b/tests/codeigniter/core/URI_test.php
index adb62f6..50663d5 100644
--- a/tests/codeigniter/core/URI_test.php
+++ b/tests/codeigniter/core/URI_test.php
@@ -135,7 +135,8 @@
 
 		$this->uri->config->set_item('enable_query_strings', FALSE);
 		$this->uri->_set_permitted_uri_chars('a-z 0-9~%.:_\-');
-		$this->uri->filter_uri('$this()');
+		$segment = '$this()'; // filter_uri() accepts by reference
+		$this->uri->filter_uri($segment);
 	}
 
 	// --------------------------------------------------------------------