moq objects Returns method, should return a null object

Question

I'm developing a Web API, and one of the test I came up with is that, if client makes a GET operation with a Physical Test ID (Physical Test is the resource I'm looking for) and that physical test is not found, the web API should return a 404 status.

Now, I'm using moq framework for my tests and I have the following code:

[TestMethod]
public void then_if_physical_test_not_found_return_not_found_status()
{
    var unitOfWork = new Mock<IUnitOfWork>();
    var repository = new Mock<IRepository<PhysicalTest>>();
    repository.Setup(r => r.FindById(It.IsAny<int>())).Returns();
    unitOfWork.Setup(m => m.PhysicalTests).Returns(repository.Object);
    var pt = new PhysicalTestResource(unitOfWork.Object);
    HttpResponseMessage<PhysicalTest> response = pt.GetPhysicalTest(43);
    Assert.AreEqual(HttpStatusCode.NotFound, response.StatusCode)
}

I need the Returns() method to return a null object, which is going to be what the actual API method would return if the resource is not found.

I tried sending null as a parameter in the Returns() method but had no success.

To clarify, the error occurs because there are two overloads of Returns, one taking T (T = IRepository<PhysicalTest> in this case) and one taking Func<T>. When passing null, the compiler doesn't know which one to use, so you have to be specific. These overloads exist to give you the option to either return a static value .Returns(new T()) or a new instance on every call .Returns(() => new T()). — JHBonarius
– JHBonarius, Commented Jul 20, 2022 at 8:25

Jeff Ogata · Accepted Answer · 2011-10-27 17:32:55Z

300

You don't indicate what the error was, but this should work:

unitOfWork.Setup(m => m.PhysicalTests).Returns((IRepository<PhysicalTest>)null);

I suspect you tried to call it with Returns(null), which causes the compiler to complain since Returns is overloaded and it doesn't know which method should be called. Casting to a specific type removes the ambiguity.

edited Oct 27, 2011 at 17:32

answered Oct 27, 2011 at 17:23

Jeff Ogata

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5 Comments

Daniel Over a year ago

it worked, but I had to make this modification: unitOfWork.Setup(m => m.PhysicalTests).Returns((PhysicalTest)null);

Jeff Ogata Over a year ago

ah, ok... I assumed that since you were trying to return repository.Object that was the type returned by PhysicalTests.

Dan Csharpster Over a year ago

I tried the same thing and I'm getting a System.NotSupportedException. {"Invalid setup on a non-virtual (overridable in VB) member: x => x.GetFoo(.value.Id)"} Any ideas?

bcr Over a year ago

@DanCsharpster You can only use Moq on interfaces or abstract classes with virtual members. Whatever class you're using that is the type of x is either a concrete class or an abstract class that has GetFoo() as non-virtual/overridable.

Jeppe Stig Nielsen Over a year ago

I can recommend this way of resolving the overload ambiguity. I just want to mention that, since the two non-generic overloads of Returns which are important here, have different names for their parameter, you can also resolve the ambiguity by writing: ... .Returns(value: null) (here value is just the name of the parameter in the overload we want, it is not a keyword).

Jorge Freitas · Accepted Answer · 2021-08-27 12:45:09Z

13

If you are receiving an error like this:

You just need to specify the input parameter of 'Returns' method. Take a look in my example:

_ = _fileStorage.Setup(x => x.LoadDocument(It.IsAny<string>())).Returns(value: null);

answered Aug 27, 2021 at 12:45

Jorge Freitas

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Comments

Paradowski · Accepted Answer · 2018-07-31 11:49:26Z

12

rt is a return type of method: FindById

repository.Setup(r => r.FindById(It.IsAny<int>())).Returns(Task.FromResult((rt)null));

edited Jul 31, 2018 at 11:49

Paradowski

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answered Jul 31, 2018 at 10:37

Radhika Patwari

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Comments

WatersLake · Accepted Answer · 2021-12-04 13:32:58Z

5

Organization is a return type of method: Get

mockCache
    .Setup(cache => cache.Get(It.IsAny<string>(), It.IsAny<string>(),It.IsAny<string>()))
    .Returns(value: null as Organization);

answered Dec 4, 2021 at 13:32

WatersLake

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Comments

Divyanshu Kareer · Accepted Answer · 2023-04-11 04:40:06Z

2

Along with casting the member to null as mentioned by the accepted answer, this approach should work as well.

unitOfWork.Setup(m => m.PhysicalTests).Returns(() => null);

answered Apr 11, 2023 at 4:40

Divyanshu Kareer

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Comments

axtck · Accepted Answer · 2021-05-23 01:54:14Z

0

You could try this:

ref1.Setup(s => s.Method(It.IsAny<Ref2>(), It.IsAny<string>()))
     .Returns((Task<Ref3>)null);

ref1 = Mock Interface
Ref2 = Type request parameter
Ref3 = Type of return method mock

edited May 23, 2021 at 1:54

axtck

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answered May 21, 2021 at 19:33

Anderson Clemente

1

Comments

Ali Jamal · Accepted Answer · 2022-04-08 12:13:27Z

0

You're too close, you only need to pass the return type as generic type like so

repository.Setup(r => r.FindById(It.IsAny<int>())).Returns<IRepository<PhysicalTest>>(null);

answered Apr 8, 2022 at 12:13

Ali Jamal

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