To give more of an insight, what I'm thinking is the following:
A phpunit.xml would already exist and would just need updating to specify the location of the PHP files in the TestPhpUnit project, or if possible, if there was a TestPhpUnit and a TestPhpUnit.Tests project was added, could it even be intelligent enough to update the phpunit.xml to the TestPhpUnit project (based on checking to see if the <name> in <name>.Tests exists as a project).
The reason being is I'd like to keep my tests outside of the project that includes the PHP code I'm working on so that when I publish the code the tests aren't included within it the code that is sent to the server.