'How to use "InternalsVisibleTo" attribute with Strongly named assembly?

I am using the "InternalsVisibleTo" attribute with an assembly to expose the internal methods/classes to my unit test project.

I now need to install that assembly into the GAC, so I need to give it a strong name. When I try doing that, I get the following error in Visual Studio.

Strong-name signed assemblies must specify a public key in their InternalsVisibleTo declarations

A bit of Googling brought me to the article below:

https://msdn.microsoft.com/en-us/library/bb763089.aspx

This article states:

"Determine the public key for the strong-named friend assembly."

This article does not say how to determine the public key. Where do I find the public key for the assembly? Also, once I have the public key, would this be the correct way to declare the attribute? 

[assembly: InternalsVisibleTo("Namespace.Assembly.Example.Name, PublicKey=ThePublicKey")]
c++sharp.net-assembly


Solution 1:[1]

UPDATE May 2019 : It works perfectly with Visual Studio 2019.

UPDATE May 2022 : as mentioned by @Igor Meszaros It also works with Visual Studio 2022.

To anyone that is using Visual Studio 2017, there is the latest method :

From our beloved IDE, go to "Tools > External Tools..." and "Add" a new tool with those settings :

  • Title : Get PublicKey
  • Command : "C:\Program Files (x86)\Microsoft SDKs\Windows\v10.0A\bin\NETFX 4.6.2 Tools\sn.exe" (/!\ choose the NETFX tool version that match your assembly NETFX version, here it's 4.6.2)
  • Arguments : -Tp $(TargetPath)
  • Check the "Use Output window" checkbox

Apply/OK those changes.

In the "Solution explorer" click on your project assembly name, and then head to "Tools > Get PublicKey". The Output window should display the (quite long) Public Key, along with the Public Token Key.

Finally, in the project that holds the internal class (i.e. the tested project) you want to expose, open the "AssemblyInfo.cs" file and add the line :

[assembly: InternalsVisibleTo("MyCompany.SolutionName.ProjectName, PublicKey=Paste your public key here")]

/!\ You have to remove the line breaks from your public key.

It worked perfectly for me, so hopefully it'll do the trick for you as well !

Solution 2:[2]

I use an old good method from classic fiction movies: "hacker always guesses password in a second attempt". It's simple technique and it doesn't require any tools besides what you already have - some unit test framework. And yes, assembly under test must be signed, as mentioned here multiple times.

Copy and paste this class below to your test DLL. It's xUnit test but the same approach works well with any unit test framework.

public class FindOutAssemblyPublicKey
{
    const string AssemblyPK = "Swordfish";

    /// <summary>
    /// Fake test to find out a correct PublicKey in InternalsVisibleTo for assembly under test.
    /// </summary>
    [Fact]
    public void AssemblyPublicKeyIsAsExpected()
    {
        byte[] publicKey = GetType().Assembly.GetName().GetPublicKey();
        var sb = new StringBuilder();
        foreach (byte @byte in publicKey)
            sb.AppendFormat("{0:x2}", @byte);

        // Set breakpoint here to find out what's in sb
        Assert.Equal(AssemblyPK, sb.ToString());
    }
}

The idea here is quite simple: test fails at first run but reveals a correct public key of the test assembly. To double check replace "Swordfish" with what you've got as actual value, run test second time to make sure it's green and here you are.

Sources

This article follows the attribution requirements of Stack Overflow and is licensed under CC BY-SA 3.0.

Source: Stack Overflow

Solution Source
Solution 1
Solution 2 Remigijus Pankevičius

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