How do I test changes to PlatformIO extension itself?

I filed an issue here:

I think I found code related to the issue (just a guess) here:

I’d love to poke around on this and see if I can find a fix, but I can’t find where this code lives on my machine (Mac, in case it matters) (I checked in ~/.vscode and ~/.platformio so far and didn’t find any other obvious places.)

Are there any pointers on where to find those files and test changes?