Creating a turn-based combat system that can also run separately

[half tundra]

I'm making a turn-based game and would like to separate the turn-based gameplay system so that it can run separately from the rest of the game so that I can test it more easily. Does Godot have any way to make a "gameplay system" (turn-based combat) that can run just the gameplay side of things by itself (without the graphics/audio/ui/etc.) but can also work inside of Godot and integrate with it (so in the actual game things that happen in the system would show in the game and it would receive controls from the game's UI)? How would I go about building something like that?

[fierce jacinth]

Make a separate scene, pass all gameplay updates through signals, then using the "run current scene" button you can just test a single scene individually