You can even do something akin to this package with the "InternalsVisibleTo" property on the assembly, so you can expose your internal classes to other specifie

You can even do something akin to this package with the "InternalsVisibleTo" property on the assembly, so you can expose your internal classes to other specified assemblies. For non-C# folks, Internal classes are normally visible only to other classes within the same assembly. This is very useful for building a tightly controlled public API while maintaining a testable code-base. This option is typically used for exposing your internal classes to a unit test project, but can also be useful for exposing to LINQPad, and could be used like the above to hand out control to other assemblies.