Personally, I find a REPL-based programming interface to be the most flexible and powerful way to interact with code.

My typical interface is that I have an editor open where I write package code, and then I have a julia REPL open beside it where I load the package (or includet the script or testset). Any changes I make with my editor to functions or structs in the package / script / testset are automatically reflected in my running julia session via Revise.jl.

I then execute the functions interactively from the REPL, introspect into data or generated code, debug, run benchmarks etc all from the REPL.

GUIs are great for many things, but they lack the flexibility I need for my day to day work.