It would be great if the test pane offered a true interactive REPL. This would allow better testing and debugging of code before publishing. Right now there always seems to be a bit of guesswork involved in getting a script runbook working correctly and being able to debug the script would be really beneficial. I am a big fan of the ISE add-on for Azure Automation, but this doesn't really offer true debugging features.
I know this is a tall order and may not be possible, but it's definitely on my wish list!
Thanks for posting this suggestion! You are right that this is a larger work item, but something that could really help with debugging. Having your & the community vote for it helps our team prioritize the work though, so even if its a tall order its great for us to get the feedback.