Resharper test runner not rebuilding?

I’ve come across this a couple of times, and it’s an awkward problem and an easy fix, so I’m letting this out into the wild, straight into the jaws of Google

The problem: Take a VS2005 solution, migrate it to Visual Studio 2008. Start running unit tests in the Resharper test runner. Change some code in the test or in the system under test and re-run the test. The code isn’t rebuilt. Blast.

Another symptom is the inability to debug your tests, even though the assembly has been built in debug mode.

The fix: Go to Build -> Configuration Manager. Whenever I’ve encountered this problem, the Active solution platform drop down has “Any CPU”, “.NET” and “Mixed Platforms”. A brand new solution (where Resharper runs as expected) only has “Any CPU”. Can you see where this is going? Yep. In the drop down, click “Edit...” and in the new dialog that appears, remove anything other than “Any CPU”. All should now work as expected.

This has been a public service announcement. And now, back to your normal working schedule.