Thursday, February 14, 2008

Getting the Data out of my Controller Tests

While working on PlanningPokerOnRails I started writing a unit test for my LoginController. The Monorail BaseControllerTest makes this easy. I am also using Rhino Mocks and Nunit. Here is the test:




The test is very simple. First, it sets a single recorded expectation that a Redirect will occur:

34 using (mocks.Record())

35 {

36 // First redirects to the index page

37 Response.Redirect("/Home/Index.rails");

38 }


Next, the playback is run and the code emulates a few things that users might do...like login with Request params for a ReturnUrl:

39 using (mocks.Playback())

40 {

41 Request.Params.Add("ReturnUrl", "/Home/Index.rails");

42 loginController.Login("dan", "danny");

43 }



Writing the Code to Pass this Test

Next I wrote the CardPlayer component (my user) and the LoginController. Seeking to do the simplest thing that could possibly work I merely had the CardPlayer inherit from the ActiveRecord base.


This made writing the controller easy, the ActiveRecord base has plenty of good methods for instantiating. I only have to call the FindOne method on the CardPlayer:


104 public static CardPlayer FindCardPlayer(string UserName,

105 string Password){

106

107 CardPlayer user = FindOne(NHibernate.Expression.Expression.And(

108 Expression.Eq("Username", UserName),

109 Expression.Eq("Password", Password)));

110 return user;

111 }


So why all the Problems?

I never intended to initialize ActiveRecord, in my tests assembly. I believe that test data should only be used for Acceptance Tests. It turns out that the test fails because no ActiveRecord config or initialization exists.


How do I solve this?

I forgot to implement good Dependency Injection. The way I would normally grab an instance of a component (like the CardPlayer) is through a service container (or repository). MVC architectures generally have two types of Model objects; Components (like the CardPlayer) and Services (like the CardPlayer Service I should have written). The services usually act like or wrap a repository of Components. In my opinion, ActiveReecord already provides the repository.

It turns out my solution is to write a CardPlayer Service container. This object will go into the IoC container (winsor) and be automatically injected into whatever controller requires it (like the LoginController). The service will use the ActiveRecordMediator to instantiate new CardPlayers and I can remove the ActiveRecordBase from my CardPlayer component.


Wait why does this help?

Well by forcing all instantiation to go through injected Services your tests can easily inject a Mock Service (I use Rhino Mocks) and tell the Mock to provide predefined instances of components. Since you have mocked the service layer you no longer need ActiveRecord in your tests!

Keeping the Data
Now that I've convinced you to write a service layer, I am going to tell you that you may not need it! While you can mock the Services going to your controllers you cannot easily get rid of ActiveRecord when testing the services. For most simple lookups a test may not be appropriate but in many cases your component lookup up and other operations will be non-trivial. For these cases you will want to test the service layer and you may have to initialize ActiveRecord.

You could decide to Mock the ActiveRecordMediator or you could use an approach similar to Oren's.


I'm Confused...

I admit that this is some advanced stuff. I promise to come back to this post and update it with more concise information.


Please leave comments on ways I can do this without a service layer. Thanks!

9 comments:

BenL said...

Not sure how this would impact your existing design or how far-reaching this refactoring might be in your application, but one alternative would be to not derive your model classes from the AR base classes and instead use something similar to the repository pattern with your repositories talking to ActiveRecordMediator or its generic equivalent.

You could then get your repositories from a service locator (or have them injected) into your domain objects if you want to follow a purist DD approach. The alternative would be to inject repositories or services (which have repositories injected into them) into your controllers. Monorail Windsor integration can do all this for you. The 2nd approach is more fitting with what I generally do.

Either way you can then mock out any interactions with your DB and test in isolation.

Agile Jedi said...

Benl,
What you descibed is exactly what I normally do. Normally, I would use the mediator in a Service container and use windsor to inject as needed. Part of me really prefers this IoC Inversion of Control) approach. What I've discovered, after talking to a colleague, is that the IoC pattern would seem to conflict with the AR pattern. Of course the AR pattern isn't the primary reason I use ActiveRecord. I use it for it's simple approach to ORM.

Right now (and this could change) I 'm tending towards the AR pattern. The argument being that I will have to initialize ActiveRecord to test the Services anyway.

I'm going to play with this more and post my examples/findings. This IoC versus AR question has become almost a philosophical dilemma.

Gareth said...

I don't think there is a one size fits all answer.

We don't have to deploy to many platforms so our environment is very stable and we have a lot of control over developer machines. Its easy for us at work to say that you have to configure a DB to run tests. On an open source project that might be a killer.

I like that article you linked to about using SQLite to do the AR tests in memory. The central point there is that you have to have a clean DB for each test for them to be isolated, atomic and repeatable.

You can argue that controller tests that use AR cant be truly atomic because they make calls to code outside the class under test. But then you have separate tests to cover the model layer. Any bugs you find in the model via controller tests were bugs you missed in the model tests.

Controllers bring a lot of model objects together into a sub system. They are glue. Maybe a unit test isn't the appropriate kind of test for glue. Maybe we should really be thinking of these as subsystem tests? If you think of it that way then it makes sense not to try and isolate the controller with mocks.

One thing that Jason brought up; when they update AR they break our stuff. If we mocked AR for model tests we wouldn't know they broke our stuff. So using it in tests helps us to continually integrate with a code base we don't control.

I think we are going down the road of doing AR + BaseControllerTest. We may look at some sort of zero config database. There are several; SQLite, Firebird. We could certainly use more testing from that end of things.

It's a conundrum to be sure.

Agile Jedi said...

Gareth,
I agree...the combination of the AR pattern and SQLite database really seems to work out best for trivial cases.

IoC is still relevant because some non-trivial service will inevitably expose itself and have nothing to do with ActiveRecord. One example is a service that loads objects from multiple sources; web service, database, etc.

As for controllers being glue. You're right they are actually a pretty classic example of the facade pattern.

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