Unit testing inheritance hierarchies with Moq

Question

I've an inheritance hierarchy which looks like the following:

public class Foo{
        public virtual IList<string> Messages{get;set;}
}

public class Foo2: Foo{
    public bool DoSomething(){
        //Evaluate something;
    }
}

public class Bar: Foo2{
    public override bool DoSomething(){
        var res = base.DoSomething();
        if(res)
            Messages.Add("Hello World");
        return res;
    }
}

My subject under test is Bar and test framework is Moq.

        [TestMethod]
        public void TestBar()
        {

            var mockedBar= new Mock<Bar>() {CallBase = true};
            mockedBar.SetupGet(x => x.Messages).Returns(new List<string>());
            mockedBar.Setup(x => x.DoSomething()).Returns(false);

            var result = mockedBar.Object.DoSomething();

            Assert.IsFalse(result, "This should fail");
            mockedBar.Verify(x => x.DoSomething(), Times.Once, "The base DoSomething is called only once.");
         }

I'm just starting to invest in unit testing and I'm not sure if I'm doing it correctly. Question:

This is passing right now but I'm not confident of my test method. The mockedBar.Setup(x=>x.DoSomething()) should setup my base.DoSomething() call. Is that correct?
How do I test that The Bar.DoSomething() is actually populating the Messages in the Foo class?

Any guidance is much appreciated.

It does not make sense to mock the object you want to test. Usually, you only mock dependencies of the object you want to test. To answer your first question: No, the setup does not setup the base method, but the method of the final object, which is a mock of Bar. — LInsoDeTeh, Sep 18 '15 at 14:07
I was actually following this [article](http://www.codenutz.com/unit-testing-mocking-base-class-methods-with-moq/). — CodeNewa, Sep 18 '15 at 14:21
Yes but the author of that article is calling a different method than the one he setups. You're trying to setup the method which you override and which just calls base. — LInsoDeTeh, Sep 18 '15 at 14:34

score 1 · Answer 1 · edited May 23 '17 at 12:22

1

In this case, I don't think you need to mock, just create a Bar object and test normally.

[TestMethod]
public void TestBar()
{
     var bar = new Bar();
     var result = bar.DoSomething();
     Assert.IsFalse(result, "This should fail");
     //I assume that this is your logic.
     Assert.IsTrue(bar.Messages.Contains("Hello World"));
}

We create a mock only when we need to stub or mock external dependencies. In your case, you don't have any external dependencies to mock.

edited May 23 '17 at 12:22

Community

1
1

answered Sep 18 '15 at 14:04

Khanh TO

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I'm testing `Bar`. So, wouldn't `Foo` and `Foo2` be the external dependencies? – CodeNewa Sep 18 '15 at 14:14
@Ashish Shakya: I don't think so. Inheritance is `is-a` relationship. Not `has-a` relationship (`has an external dependency`). The inherited properties become the part of an object itself, when there is any change in `Foo` or `Foo2` that breaks your code in `Bar`, unit test should detect that. – Khanh TO Sep 18 '15 at 14:15

score 1 · Answer 2 · answered Sep 18 '15 at 14:05

You are setting up a mock and then calling that same mock with this code:

mockedBar.Setup(x => x.DoSomething()).Returns(false);
var result = mockedBar.Object.DoSomething();
Assert.IsFalse(result, "This should fail");

So this doesn't actually call or test your code.

For the example here, I would either not use mocking at all and just test the whole stack or if you can change the code that you are testing, I would look at using dependency injection to remove this inheritance.

Using inheritance to share code makes testing much more difficult.

Thanks for confirming my thoughts. I was afraid that I was not testing anything at all. I'll look into the DI workaround as well. Thank you. — CodeNewa, Sep 18 '15 at 14:18

Unit testing inheritance hierarchies with Moq

2 Answers2