Testing Friendly and Internal Methods
If you're doing Test Driven Development (TDD), you want to test all the methods and properties on your classes. However, some of those methods may only be intended to be used by other classes within the same class library. If so, the right thing to do is declare those methods as either Friend (Visual Basic) or internal (C#). The problem is that those methods won't be visible to your test code running in your separate test project.
The good news is that you don't have to make these methods public to test them. Instead, if you add the InternalsVisibleTo attribute to your project's Assemblyinfo file (or any source code file), you can specify that your test project has access to your project's friendly/internal members.
This example makes the internal/friendly members of the project visible to another project called MyTest:
<Assembly: System.Runtime.CompilerServices.InternalsVisibleTo("MyTest")>
If you use the Unit Test Wizard in Visual Studio 2010, it will add this attribute to your AssemblyInfo file for you. Unfortunately, the Wizard adds the attribute at the end of the AssemblyInfo file where it won't work: the InternalsVisibleTo attribute must immediately follow any Imports or using statements at the top of the file. Visual Studio has an error correction option that will do this for you -- just click on the error block underneath the attribute to get Visual Studio to relocate it.
Posted by Peter Vogel on 05/09/2014