Is it possible to prevent a Ruby instance from opening network connection?

I maintain a web API written in Ruby. It connects to many third party web services. When writing tests, I stub any function that would need to connect to the network and return bottled data instead.

It has happened to me before that I forget this stubbing step, and my integration tests end up actually connecting to a third party service.

With that in mind, I would like to prevent Ruby from being able to open network connections. When attempted, I would like it to raise an exception instead, pointing out what function I forgot to stub.

Is this possible? What central Ruby function would I need to override to achieve this with minimal other side effects?