WebApplicationProxy.cs GetHttpApplicationType() exception

Just by doing this in my xUnit test:
[Fact]
public void TestMethod1()
{
WebApplicationProxy.Create(typeof(Studio.StudioLogin));
}

I am getting this exception in WebApplicationProxy.cs GetHttpApplicationType() method.

'_Instance._compiler.GetCompiledType("/Default.aspx")' threw an exception of type 'System.Web.HttpException'

A bit more detail - System.InvalidOperationException : The WebApplicationProxy has not been created and initialized properly

So it seems like I'm missing some crucial step here. Is there something wrong with the web application? It is a rather old and complicated legacy application with some non-standard techniques being used.
@csharpfritz