Question

I have a third party component that I am trying to write unit tests around. The problem is that I can’t mock the object and there is no interface.

I decided to create an interface and a wrapper class calling into the code for the sake of mocking. I looked into the class definition that is generated by Visual Studio using the meta data and noticed a few things:

• The class has two constructors (one takes a parameter)
• The class inherits from IDisposable

My questions are:

1. Does my implementation below look right?
2. Did I handle the IDisposable implementation correctly in the proxy class?
3. Do I need the second constructor in the proxy class since the interface does not support constructor definitions? I use dependency injection in my code and I assume unless I tell my DI framework to use the second constructor I don’t really need it but I am not sure.

The meta data looks like (slimmed down version):

public class PopClient : IDisposable
{
    public const int DefaultPort = 110;
    public const int DefaultSSLPort = 995;

    public PopClient();
    public PopClient(AddressFamily addressFamily);
    public bool HasTimeStamp { get; }
    public List<string> Capability();
    public void Connect(string host);
    protected override void GetServerGreeting();
}

Based on the meta data, my interface looks like (after removing methods/properties/access modifiers that are invalid in an interface definition):

public interface IPopClient : IDisposable
{
    bool HasTimeStamp { get; }
    List<string> Capability();
    void Connect(string host);
    void ConnectSSL(string host);
}

Based on the interface, I then created the wrapper class:

public class PopClientProxy : IPopClient
{
    private readonly Pop3 pop3;

    public PopClientProxy()
        this.pop3 = new Pop3();

    public PopClientProxy(AddressFamily addressFamily)
        this.pop3 = new Pop3(addressFamily);

    public bool HasTimeStamp
        get { return pop3.HasTimeStamp; }

    public List<string> Capability()
        return pop3.Capability();

    public void Connect(string host)
        pop3.Connect(host);

    public void Dispose()
    {
        if (pop3 != null)
            pop3.Dispose();
    }
}

Answer 1

Your proxy looks fine. Based on it, it should be very easy to mock the relevant parts of the interface your tests are dealing with.

About the IDisposable implementation, take a look at the disposable pattern common practices. This question is about it.

And for the constructor(s), I’d say that they simply aren’t part of the interface and, as such, don’t need to be replicated in implementations of the proxy. If that leads to strange constructor logic in your DI container, try separating construction from initialization and include the latter in the interface.