How to test if HttpClient has a client certificate included?

Question

I have an implementation of an authenticated HttpClient generator class that resembles this:

public class X509Authentication : IClientAuthenticator
{
    protected readonly X509Certificate2 Certificate;

    public X509Authentication(X509Certificate2 certificate)
    {
        if (certificate == null) throw new ArgumentNullException("certificate");
        Certificate = certificate;
    }

    public HttpClient GenerateClient()
    {
        var clientHandler = new WebRequestHandler();
        clientHandler.ClientCertificates.Add(Certificate);
        var request = new HttpClient(clientHandler);
        return request;
    }
    public void Dispose()
    {
        //nothing to do here.
    }
}

... how can I test that the GenerateClient() method has successfully attached the client certificate to the HttpClient class?

[TestMethod]
public void HttpClientCreationIncludesCertificate()
{
    using (var auth = new X509Authentication(_certificate))
    using (var client = auth.GenerateClient())
    {
        Assert...what?  The certificate(s) are not visible here.
    }
}

...or am I trying to test the wrong thing?

Answer 1

9 month old question but anyhow :)

What I would do. You are thinking correctly with the interface. Now that you have an interface you can mock away the "real" implementation of GenerateClient since this method doesn't do anything else then using someone else's code (Code that that's not very test-friendly in the first place).

What I would test in this situation is that the method that should call IClientAuthenticator.GenerateClient really calls it. An example ->

[TestMethod]
Public void MyClass_MymethodthatcallsGenereateClient_DoesCallGenerateClient()
{
    // Arrange
    Mock<IClientAuthenticator> clientAuth = new Mock<IClientAuthenticator>();
    MyClass myclass = new MyClass()

    // Act
    var result = MyClass.MymethodthatcallsGenereateClient();

    // Assert (verify that we really added the client)
    clientAuth.Verify(x => x.GenerateClient);
}

Now we can be safe knowing that the client certificate is added when it should be. Hope this helps!