How can I default VS Test Processor Architecture to x64?

Question

I depend on a mixed-mode assembly which is compiled for x64. Because I do not want warnings in my build, all of the projects in my solution target x64 directly--they are not An

Answer 1

UPDATE FOR VS2017:

It seems that after opening the solution, when you click on the “Test Explorer” tab in Visual Studio, this rebuilds your tests. The “Run Test(s)” and “Debug Test(s)” menus become visible and enabled, as well as the checkbox next to previously selected “x64” option also gets restored.

The "Default Processor Architecture" menus option selected still seem to be cleared on close down of Visual Studio but the above action does seem re-select the previously selected option.