How can I test Swift files in Xcode using XCTest without having to build the entire app?

What I'm trying to do is test a Swift file frequently after making tiny changes to the file. The file may contain one or more structs and classes.

I don't care about a concept of an "app" because this is purely an academic exercise to practice some new concepts I've learned. I just want to test the file and don't care about the app and anything related to the app.

You may be asking why? Speed. I want it to be really fast to test, right now it takes a few seconds for the most trivial example. I see it does a lot of work to build the targets: