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
UPDATE FOR VS2015:
To ensure your test projects run at x64 please do the following:
Then...
Right-click your test project from the solution explorer and select 'Properties'
Select the 'Build' tab on the left
Change the Target Platform to x64
Note that you might get BadImageFormatExceptions if you are targetting a different platform for your live project. For example if Project1 is x86 and your Project1Test is targetting x64 you will likely come across this issue. You'll need to make sure both are matching (or just select 'Any CPU').
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.
On Visual Studio 2013 I found that after setting "Default Process Architecture" to X64 I'll go and open "Options..." and close it with "OK", then the "Default Process Architecture" will preserved, at least for this one solution.