Add truffle spec until Joni is fixed

Author: eregon

spec/truffle/regexp_spec.rb

@@ -0,0 +1,16 @@
+# Copyright (c) 2020 Oracle and/or its affiliates. All rights reserved. This
+# code is released under a tri EPL/GPL/LGPL license. You can use it,
+# redistribute it and/or modify it under the terms of the:
+#
+# Eclipse Public License version 2.0, or
+# GNU General Public License version 2, or
+# GNU Lesser General Public License version 2.1.
+
+require_relative '../ruby/spec_helper'
+
+describe "Regexp" do
+  it "raise a RegexpError and not a fatal error when it fails to parse in Joni" do
+    # On MRI this actually does not raise, but we need to fix Joni first for that
+    -> { Regexp.new("\\p{") }.should raise_error(RegexpError)
+  end
+end