One Project in Solution bold face - why?

[loonquawl]

I recently noticed that one of the projects in my Solution is written bold - does anyone know what that signifies? I'm stumped. The repositories of each project are bold too, but at least they all are.
That single project is not special in any way i see. It's not currently open, it's Git status is the same, it's in Debug like all the others - ?

[Stub]

That's the project flagged as the "StartUp Project". Right-click any of your projects and change it via the context menu. It'll be the test suite that runs when you press the Run button.

[loonquawl]

Thank You!