xUnit test Uwp project get 'Unsupported MRT profile type' exception

I am trying to test a UWP project with xUnit.
On create instance of Windows.ApplicationModel.Resources.ResourceLoader(), I get exception: Unsupported MRT profile type. (Exception from HRESULT: 0x80073B20)
Example method to test:

public int Sum(int a, int b)
{
    var loader = new Windows.ApplicationModel.Resources.ResourceLoader();
    return a + b;
}

With MsTest test is passed.