Unit Testing - Session object?

Question

I have recently Implemented a unit of work pattern, and as an environment we are using more unit testing. Currently the implementation writes into a session helper that writes to session. How do I unit test these aspects in regard to the session? Should I make a repository pattern? (repository interface with concrete session implementation and concrete mock implementation) How is this normally done?

I know there is probably more than one way of approaching this, but I am just looking for some advice.

Rob Stevenson-Leggett Rob Stevenson-Leggett · Accepted Answer · 2011-07-01T13:38:28

There are basically two ways of doing this.

Assuming you are using .NET 3.5 or up. Change your implementation to take the HttpSessionStateBase object as a constructor parameter, you can then mock this implementation - there's a few tutorials online on how to do this. You can then use an IoC container to wire this up at app start or do something like (poor man's dependency injection):

public class MyObjectThatUsesSession
{
    HttpSessionStateBase _session;

    public MyObjectThatUsesSession(HttpSessionStateBase sesssion)
    {
         _session = session ?? new HttpSessionStateWrapper(HttpContext.Current.Session);
    }

    public MyObjectThatUsesSession() : this(null)
    {}
}

Alternatively, and probably a bit better and more flexible design would be to create a test seam by wrapping your interaction with session in another object. You could then change this to a database, cookie or cache based implementation later. Something like:

public class MyObjectThatUsesSession
{
    IStateStorage _storage;

    public MyObjectThatUsesSession(IStateStorage storage)
    {
         _storage= storage ?? new SessionStorage();
    }

    public MyObjectThatUsesSession() : this(null)
    {}

    public void DoSomethingWithSession()
    {
        var something = _storage.Get("MySessionKey");
        Console.WriteLine("Got " + something);
    }
}

public interface IStateStorage
{
    string Get(string key);
    void Set(string key, string data);
}

public class SessionStorage : IStateStorage
{
    //TODO: refactor to inject HttpSessionStateBase rather than using HttpContext.

    public string Get(string key)
    {
       return HttpContext.Current.Session[key];
    }

    public string Set(string key, string data)
    {
       HttpContext.Current.Session[key] = data;
    }
}

You can then use Moq to create a mock IStateStorage implementation for your tests or create a simple dictionary based implementation.

Hope that helps.

Unit Testing - Session object?

2 Answers