[Chore] More readable functions

[kyungeunni]

Summary

There are a few functions in the codebase that is quite long so that it is quite difficult to comprehend the changes whenever we update or make a fix.

For instance, onTest function in electron/execution.ts is 163 lines long and it contains several nested functions and the inlined logic mixed up together. It'd be easier to maintain and review the code if we can divide up the code into smaller chunks, even into a separate file if it deserves it. The good example is #256. It was a quite small bug fix but I needed to extend most of the collapsed part of the code when reviewing as I wasn't sure if the change is part of the main logic or applied to a nested helper / utill function.

Why is this important?

It'd help us understand and maintain the code better and easier.