I tend to code exactly this way - vi in one terminal, and <up-arrow><enter> in another terminal (tmux, actually) to test it. I will definitely be trying this out since it would save me a lot of tapping and clicking when I'm experimenting or refactoring.
You should have a donation link. I've been fiddling with gaze off and on this eve. I love that I can simply write a quick test under my (defun ...) and then :w, which is already my habit, to see if it works. This erases all the hubbub I have to do in between saving and testing. A perfect niche. Gaze exactly soothes a common pain point.
It is going to be part of my workflow, and at least worth a beer or highly caffeinated beverage.