How to mock a function call on a concrete object with Moq?

Question

How can I do this in Moq?

Foo bar = new Foo();
Fake(bar.PrivateGetter).Return('whatever value')

It seems I can only find how to mock an object that was created via the framework. I want to mock just a single method/property on a concrete object I've created.

In TypeMock, I would just do Isolate.WhenCalled(bar.PrivateGetter).Returns('whatever value').

Any ideas?

score 57 · Answer 1 · edited Mar 12 '13 at 08:03

57

You should use Moq to create your Mock object and set CallBase property to true to use the object behavior.

From the Moq documentation: CallBase is defined as “Invoke base class implementation if no expectation overrides the member. This is called “Partial Mock”. It allows to mock certain part of a class without having to mock everything.

Sample code:

    [Test]
    public void FailintgTest()
    {
        var mock = new Moq.Mock<MyClass>();
        mock.Setup(m => m.Number).Returns(4);
        var testObject = mock.Object;
        Assert.That(testObject.Number, Is.EqualTo(4));
        Assert.That(testObject.Name, Is.EqualTo("MyClass"));
    }

    [Test]
    public void OKTest()
    {
        var mock = new Moq.Mock<MyClass>();
        mock.Setup(m => m.Number).Returns(4);
        mock.CallBase = true;
        var testObject = mock.Object;
        Assert.That(testObject.Number, Is.EqualTo(4));
        Assert.That(testObject.Name, Is.EqualTo("MyClass"));
    }

    public class MyClass
    {
        public virtual string Name { get { return "MyClass"; } }

        public virtual int Number { get { return 2; } }
    }

edited Mar 12 '13 at 08:03

gsk

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answered Mar 17 '10 at 13:46

Ariel Popovsky

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Thanks, I will try this. Makes TypeMock look more and more tempting though. Ugh! – dferraro Mar 17 '10 at 19:14
1

This didn't work - it gave error message on the mock.Setup() line (in second example) "Test method CRMFundOfFundPluginsUnitTest.FoFPluginBaseTest.SetMissingTargetValuesTest1 threw exception: System.ArgumentException: Invalid setup on a non-overridable member: m => m.InputTargetDE.". Any idea why? – dferraro Mar 18 '10 at 19:56
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Make sure the methods you are mocking are virtual so Moq will be able to override them. – Ariel Popovsky Apr 12 '10 at 14:58
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This doesn't actually answer the question. -- This calls base methods, but it requires that you let Moq create the object. -- The scenario that the OP showed has something externally creating the mock object. – BrainSlugs83 Feb 24 '17 at 22:07
Doesn't answer the question maybe, but it is close enough for many situations and solved the problem for me. – Martin Capodici Jul 20 '17 at 06:36

score 13 · Accepted Answer · edited May 23 '17 at 10:31

13

Only TypeMock Isolator (and perhaps Moles) can perform these stunts. Normal dynamic mock libraries can only mock virtual and abstract members.

edited May 23 '17 at 10:31

Community

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answered Mar 17 '10 at 13:45

Mark Seemann

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Good to Know - wish there was more info on Moles out there - haven't heard anything on it at all yet as far as people using it here on SO – dferraro Mar 17 '10 at 19:15
FWIW, here's the official site: http://research.microsoft.com/en-us/projects/moles/ – Mark Seemann Mar 17 '10 at 19:51
That Moq cannot do this is simply not true anymore. – MushinNoShin Sep 30 '14 at 23:57
@MushinNoShin Oh, I didn't know that! Can you provide a link? – Mark Seemann Oct 01 '14 at 10:06
Check the most upvoted answer in this question :) It only works if there's a parameterless constructor available however, which is the case for this question. – MushinNoShin Oct 03 '14 at 17:33
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@MushinNoShin Yes, and make sure to also read the comments from the OP: "This didn't work". That answer explains how to Moq virtual members, whereas the OP asks about private members. The link in my (accepted) answer explains what is technically possible. – Mark Seemann Oct 04 '14 at 09:58
@MarkSeemann Ah, you're right, I guess I glossed over the `bar.PrivateGetter` part. Thanks! – MushinNoShin Oct 04 '14 at 14:02

score 3 · Answer 3 · answered Mar 20 '10 at 03:50

Moles can also replace private methods as long as the types on the signature are visible. So in this case, it would look like this:

MFoo bar = new MFoo { // instantiate the mole of 'Foo'
    PrivateGetterGet = () => "whatever value" // replace PrivateGetter {get;}
};
Foo realBar = bar; // retrive the runtime instance
...

If you are looking for more information on Moles, start with the tutorials at http://research.microsoft.com/en-us/projects/pex/documentation.aspx.

How to mock a function call on a concrete object with Moq?

3 Answers3

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