Targeting a non-public xUnit fixture fails silently

[jcansdale]

For example:

    class OopsNonPublic
    {
        [Fact]
        public void Test()
        {
        }
    }

Simply shows:

------ Test started: Assembly: ConsoleApp8.dll ------

xUnit.net .NET CLI test runner (64-bit .NET Core win10-x64)

It would be good to say something more helpful.