Testdriven.NET can't find assembly for project with VS2015 and Xunit

I can successfully run Xunit tests in a VS2015 project from the command line with:

dnx test

but when attempting to use Testdriven.NET from within Visual Studio, it is returning a message Can't find assembly for project. Also the Visual Studio Test Explorer doesn't seem to be finding the tests either.

Presumably the tests are constructed correctly if they run from the command line, so I was wondering what else might be missing.