If the application is well-structured, you can run many types of tests without ever touching the UI. You can also run things like linters and static analysis tools (although those are usually platform-agnostic).

Seems like if linked libraries weren’t present, GUI or no, it would be problematic. Im a hardware guy though so not much experience with that.

This isn't my exact area either, so my terminology is probably off, but one way to do this would be to compile the "backend" code separately and run unit tests on that. Treat it as a library in your application, if you will.

Another approach I've heard used was just faking the library from the headers - as long nothing from it is called in the course of your testing, your program wouldn't notice.