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` in this case) and one taking `Func`. 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, Jul 20 '22 at 08:25

Jeff Ogata · Accepted Answer · 2011-10-27T17:32:55.190

286

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 '11 at 17:32

answered Oct 27 '11 at 17:23

Jeff Ogata

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10

it worked, but I had to make this modification: unitOfWork.Setup(m => m.PhysicalTests).Returns((PhysicalTest)null); – Daniel Oct 27 '11 at 17:26
1

ah, ok... I assumed that since you were trying to return `repository.Object` that was the type returned by `PhysicalTests`. – Jeff Ogata Oct 27 '11 at 17:30
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? – Dan Csharpster Jan 17 '17 at 18:07
@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. – bcr Feb 22 '17 at 20:07
1

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). – Jeppe Stig Nielsen Dec 11 '18 at 14:16

score 12 · Answer 2 · edited Jul 31 '18 at 11:49

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 '18 at 11:49

Paradowski

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answered Jul 31 '18 at 10:37

Radhika Patwari

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score 10 · Answer 3 · answered Aug 27 '21 at 12:45

10

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 '21 at 12:45

Jorge Freitas

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score 5 · Answer 4 · answered Dec 04 '21 at 13:32

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 04 '21 at 13:32

WatersLake

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score 1 · Answer 5 · answered Apr 11 '23 at 04:40

1

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 '23 at 04:40

Divyanshu Kareer

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score 0 · Answer 6 · edited May 23 '21 at 01:54

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 '21 at 01:54

axtck

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answered May 21 '21 at 19:33

Anderson Clemente

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score 0 · Answer 7 · answered Apr 08 '22 at 12:13

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 08 '22 at 12:13

Ali Jamal

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moq objects Returns method, should return a null object

7 Answers7