InternalsVisibleTo attribute isn't working

Question

I am trying to use the InternalsVisibleTo assembly attribute to make my internal classes in a .NET class library visible to my unit test project. For some reason, I keep getting an error message that says:

'MyClassName' is inaccessible due to its protection level

Both assemblies are signed and I have the correct key listed in the attribute declaration. Any ideas?

Answer 1

You need to use the /out: compiler switch when compiling the friend assembly (the assembly that does not contain the InternalsVisibleTo attribute).

The compiler needs to know the name of the assembly being compiled in order to determine if the resulting assembly should be considered a friend assembly.

Answer 2

Are you absolutely sure you have the correct public key specified in the attribute? Note that you need to specify the full public key, not just the public key token. It looks something like:

[assembly: InternalsVisibleTo("MyFriendAssembly, PublicKey=0024000004800000940000000602000000240000525341310004000001000100F73
F4DDC11F0CA6209BC63EFCBBAC3DACB04B612E04FA07F01D919FB5A1579D20283DC12901C8B66
A08FB8A9CB6A5E81989007B3AA43CD7442BED6D21F4D33FB590A46420FB75265C889D536A9519
674440C3C2FB06C5924360243CACD4B641BE574C31A434CE845323395842FAAF106B234C2C140
6E2F553073FF557D2DB6C5")]

i.e. 320 or so hex digits. Not sure why you need to specify the full public key - possibly with just the public key token that is used in other assembly references it would be easier for someone to spoof the friend assembly's identity.

Answer 3

It is worth noteing that if the "friend" (tests) assembly it is written in C++/CLI, rather than C#/VB.Net then you need to use the following:

#using "AssemblyUnderTest.dll" as_friend

instead of a project reference or the usual #using statement. For some reason, there is no way to do this in the project reference UI.

Colin

Answer 4

You can use AssemblyHelper tool that will generate InternalsVisibleTo syntax for you. Here's the link to the latest version.

Answer 5

If your assemblies aren't signed, but you are still getting the same error, check your AssemblyInfo.cs file for either of the following lines:

[assembly: AssemblyKeyFile("")]
[assembly: AssemblyKeyName("")]

The properties tab will still show your assembly as unsigned if either (or both) of these lines are present, but the InternalsVisibleTo attribute treats an assembly with these lines as strongly signed. Simply delete (or comment out) these lines, and it should work fine for you.