Running a 64 bit unit test

This tells how to set processor architecture for unit tests, but my problem is that despite following the recommended

choose Test, then choose Settings, and then choose Processor Architecture. Choose x64

my unit test is not appearing in the Test Explorer list anymore. When I set the test to Any CPU, the test entry shows up in Test Explorer, but it is x86 and does not run properly. It is critical that this specific unit test must run in x64 mode, as it uses x64 specific features (more than 4 GB per process).

I am using 15.5.3 if that matters.