Test for proper handling of incomplete hex escapes (#1274)

See relevant firefox bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1408452

test/built-ins/RegExp/incomplete_hex_unicode_escape.js

@@ -0,0 +1,18 @@
+// Copyright (C) 2015 Zirak. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+description: An incomplete HexEscape or UnicodeEscape should be treated as an Identity Escape
+info: >
+    An incomplete HexEscape (e.g. /\x/) or UnicodeEscape (/\u/) should fall
+    through to IdentityEscape
+esid: prod-AtomEscape
+---*/
+
+// Hex escape
+assert(/\x/.test("x"), "/\\x/");
+assert(/\xa/.test("xa"), "/\\xa/");
+
+// Unicode escape
+assert(/\u/.test("u"), "/\\u/");
+assert(/\ua/.test("ua"), "/\\ua/");