Excellent - I hadn't thought of going down a level and that makes a lot of sense. I'm still exploring how best to do this but you've certainly given me a jump start. As I was using the Mojo::UserAgent I had a quick sniff at Mojo::UserAgent::Mockable but I'm not yet convinced that this is the way to go. Although it looks perfect in a way, I have concerns about it breaking tests in some environments.

Most of my concern stems from the very long install time locally and the number of dependencies suggesting it might be a little heavy just to provide a test capability. I haven't written it off entirely as an option though but will focus my attention initially on injecting responses similar to your suggestion.

Thanks heaps for the tips and insight from your experience