I'm intrigued by Amazon LEX for building a bot but at the same time love the ease of Firebase. Is there a similar product on Google? Maybe accessible via Google Cloud Function?
Google owns api.ai. That seems to provide the closest functionality to Lex. Hopefully that gives you something to look into.
Also, I haven't done this personally, but it seems like an article that might help you: http://glaforge.appspot.com/article/a-tight-develop-test-loop-for-developing-bots-with-api-ai-the-google-cloud-function-emulator-node-js-and-ngrok