VS2012, Python 2.7 32-bit & 64-bit installed, PTVS 2.0 Beta
Set your default interpreter to be 2.7 32-bit
Create new python app
Add new item, unit test
Change the code of the test to be:
arc = str(platform.architecture())
print('architecture=' + arc)
self.assertTrue('32bit' in arc)
Run the test, it should succeed.
Set your default interpreter to be 2.7 64-bit, using the Interpreters tool window
Run the test again, it will succeed. Look at the output for the test, it will be 32-bit.
It should have failed. It didn't use the new default interpreter.
Restart VS, reload the solution and run the test again, it will use the correct interpreter (64-bit) and fail, as expected.