Visual Studio unit test project cannot see most of my scripts

I am using Visual Studio to unit test my C# scripts, but most of my classes cannot be referenced.

I created at Unit Test Project in Visual Studio 2013 Ultimate and added the Library\ScriptAssemblies\Assembly-CSharp.dll as a reference. There are a couple of classes defined in my scripts that can now be referenced. Unfortunately most of them cannot be.

It looks as if all the classes that extend MonoBehavior can be referenced, and a couple that do not.

I would like to know why this is, and what I can do to fix it, please.

It must be that Assembly-CSharp.dll is not being updated, right? But, if so, what is it that causes it to update? Clean + Build in Visual Studio does not seem to do it, nor does building the project in Unity.