Unit tests discovered, but not running in VS 2015

I am trying to use the Unit Test Manager feature of Visual Studio 2015 Community Edition, and it discovers the tests successfully; however, when trying to run the tests (either by using the "Run All" option, or by right-clicking and selecting "Run selected tests"), the test is never run; the green progress bar at the top scrolls across indefinitely.

Initially I thought it was a problem with the C++ unit testing suite specifically, but I have just tried it with the Python unit tests too, and I am encountering the same problem. Does anyone have any workarounds, or is this even a known issue with Visual Studio 2015?