Unit testing levels of classes with Nunit and Nmock

Question

I have levels of classes and interfaces, namely Level1, Level2 and Level3.
Class Level1 depends on class Level2 and class Level2 depends on class Level3.

Here is the code for that design:

public interface ILevel1
{
    string GetData();
}

public class Level1 : ILevel1
{
    ILevel2 level2;
    public Level1(ILevel2 level2)
    {
        this.level2 = level2;
    }

    public string GetData()
    {
        // some more process on data.
        var data = level2.GetDataAndProc();
        data = data + ",Proc at Level1";
        return data;
    }
}

public interface ILevel2
{
    string GetDataAndProc();        
}

public class Level2 : ILevel2
{    
    ILevel3 level3;
    public Level2(ILevel3 level3)
    {
        this.level3=level3;
    }

    public string GetDataAndProc()
    {
        var data=level3.GetDataFromDB();
        // processing on the data from db.
        data=data+ " Processed at level2";
        return data;
    }
}

public interface ILevel3
{
    string GetDataFromDB();
}

public class Level3 : ILevel3
{
   public string GetDataFromDB()
   {
       // Functionalities to get data from db.
       return "DB Data";
   }
}

Now, I can unit test class Level1 in isolation mocking Level2 interface and unit test class Level2 in isolation mocking Level3 interface. I am using Nunit as testing framework and NMock as mocking framework.

So far so good.

But, can I unit test first two levels of code only mocking Level3 interface without mocking Level2? I mean I want to unit test class Level1 without mocking Level2 but mocking Level3. I wanted to do this because Level3 class gets data from DB and I want to mock only this DB layer so that my whole project works just with mock db not with real db.

Answer 1

That is easy:

// arrange
var mocks = new Mockery();
var mockLevel3 = mocks.NewMock<ILevel3>();
// now do some actual mocking here

var level2 = new Level2(mockLevel3);
var level1 = new Level1(level2);

// now do some act and assert stuff

It is an integration test in my opinion. It does not matter at this point if all of the classes are in the same assembly. Integration tests are not necessarily about bringing together some assemblies in a test.