title: Add a unit test project to an existing Qt Creator project
body: <p>I have an existing Qt Creator project which is not a Subdirs project. I have now reached a point where I want to add a unit test project to it. When I create the new unit test project, the "Add as a subproject to..." combo is disabled.</p>
  
  <p>How can I do it? I'm thinking about creating a brand new Subdirs project and adding my existing project to it, and then adding the unit test project as well.</p>
  
  <p>Is that how it should be done or is there a better way?</p>