Testing Conversational AI Chatbots - What automation tools are there?

Does anyone have any experience with testing chatbots (web messaging bots) using automation tools?

I have come across Botium and will be doing some research into this, but is anyone aware of any other automation framework tools out there? I am especially interested in any free opensource tools, but am open to any ideas and suggestions you may have.

I look forward to hearing about any experience you have had either using the tools or from any research you may have done.