Karl Seguin

UPDATE: I solved my problem by marking my method as protected internal instead of just internal.

My adventures through TDD land aren't over yet. I decided to follow Joshua's and Jeremy 's advice and spend some time looking into RhynoMocks.

As you may recall, in Lesson 3 I decided to start testing near my database boundary by using a factory provider and creating a fake/test implementation. Basically, instead of actually hitting a database, I would store values in memory. It worked really well, but it did require a lot of work - and sometimes I had to spend time thinking about and planning my fake implementation.  I now realize that on top of the extra work, I was also testing a lot more than just "units" of code.

So I downloaded RhinoMocks. There's definitely a small learning curve - not sure if it's technical or mental. After a bit of playing with it, I'm really getting into it.

So sticking with the example we've been working on, let's change our DataProvider to a concrete class which relies on an IDataStore implementation to do the database interaction. Our DataProvider now looks something like:

public class DataProvider
{
    private IDataStore _store;

    public DataProvider()
    {
       //this is our actual store, which we default to
       _store = new SqlDataStore();
    }
    internal DataProvider(IDataStore store)
    {
        //override the default store...say for testing!
        _store =store;
    }
    public List<Indicator> GetAllIndicators()
    {
        List<Indicator> indicators =  _store.GetAllIndicators();
        if (indicators == null)
        {
           indicators = new List<Indicator>();
        }
        return indicators;
    }
}

Looking at GetAllIndicators (yes, I wrote the code BEFORE writing the test, *tisk*), I see at least 2 things I want to test - the store's GetAllIndicators() is called and null is never returned. At first I thought I wanted to test more than just the interaction between my DataProvider and the store, but I quickly realized that (a) my TestDataProvider didn't really test anything more since the implementation isn't real and (b) I'm unit testing DataProvider, not my store.

So I write my unit test:

[Test]
public GetAllIndicatorsReturnsEmptyListInsteadOfNull()
{
   MockRepository mock = new MockRepository();
   IDataStore store = (IDataStore)mock.CreateMock(typeof(IDataStore));
   //inject my mock object
   DataProvider provider = new DataProvider(store);
  
   Expect.Call(store.GetAllIndicators()).Returns(null);
   mock.ReplayAll();
   Assert.IsNotNull(provider.GetAllIndicators());
   mock.VerifyAll();
}

I create a mock implementation of IDataStore - as you can see, I've already gained a lot by not having to implement my own test version. I then say that I expect a call to my mock object and that it ought to return null. Then I go into replay mode, actually execute the code I want to test and verify my expectations.

Now, suppose I wanted DataProvider.GetAllIndicators to cache the results (I know, i know..caching has it's ups and downs...). I would only expect 1 call to store.GetAllIndicators..so I write my test:

[Test]
public GetAllIndicatorsIsCached()
{
   MockRepository mock = new MockRepository();
   IDataStore store = (IDataStore)mock.CreateMock(typeof(IDataStore));
   //inject my mock object
   DataProvider provider = new DataProvider(store);
  
   Expect.Call(store.GetAllIndicators()).Returns(new List<Indicator>());
   mock.ReplayAll();
   Assert.IsNotNull(provider.GetAllIndicators());
   Assert.IsNotNull(provider.GetAllIndicators());
   mock.VerifyAll();
}


The only things I've changed are:
  - Return new List<Indicator>() instead of null (not really necessary), and
  - Call provider.GetAllIndicators TWICE

I run the test and it fails. I get an error saying store.GetAllIndicators was expected to be called once, but it was called twice. So I go into my code and add the caching logic:

public List<Indicator> GetAllIndicators()
{
   string cacheKey = "DataProvider:GetAllIndicators"; 
   List<Indicator> indicators =  (List<Indicator>)HttpRuntime.Cache[cacheKey];
   if (indicators == null)
   {
       indicators =  _store.GetAllIndicators();
       if (indicators == null)
       {
           indicators = new List<Indicator>();
       }
       HttpRuntime.Cache.Insert(cacheKey, indicators, null, DateTime.Now.AddMinutes(10), Cache.NoSliddingExpiry);
   }
   return indicators;
}

And my test now passes because _store.GetAllIndicators is only called once.

All in all, I'm very impressed. I was having a problem mocking a class object that had an internal virtual member. I did use [assembly: InternalsVisibleTo(RhinoMocks.StrongName)], but as soon as I tried to create my mock object, I was getting an exception deep inside RhinoMocks about implementing or overriding a member that wasn't visible/accessible...I don't remember the exact message, but if anyone can help me out, I'd appreciate it!

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