Target MacNativeUTITest should build and then run from the Applications folder. Once it's run, the file extension .customuti should be associated with the app.

Target MacCatalystUTITest should be run as a Catalyst app. Theoretically, using the same process as above, the file extension .customuti2 should be associated with the app, but none of my tests have led to this association successfully.

There are sample .customuti and .customuti2 in the repo to test with.