TDD Lesson 4 – I mock you (updated)

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]

   IDataStore store = (IDataStore)mock.CreateMock(typeof(IDataStore));
   //inject my mock object

}

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];

   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!

[tags: Agile, TDD, .NET]