Can't debug test using breakpoint in Visual Studio 2013

I'm trying to debug a failing unit test by putting a breakpoint at the beginning of the test method and choosing Debug Selected Tests in the Test Explorer. However, the test always runs (and fails) without hitting the breakpoint.

I've tried:

• Cleaning and rebuilding the project


• Restarting Visual Studio

This seems like a pretty basic case - I'm not attaching to a separate process, or doing anything fancy. Just a basic unit test inside VS2013. What else can I try to get the debugger to work correctly?