Method without setup not return null

[michelcedric]

Hi,
I make a MockTestCase project : https://github.com/michelcedric/MockTestCase/blob/master/MockTest/UnitTest1.cs

When a method without setup is defined normaly he returns null.
But If the return it's a IEnumerable, it's return an empty list.

I think it's a strange behavior and I don't understand why not return null?

Best regards

Cédric Michel

[stakx]

Apologies, I misread your above post. This doesn't look like a duplicate.

[michelcedric]

Setups with no .Returns(…) nor .CallBase() no longer return default(T) for loose mocks, but a value that is consistent with the mock's CallBase and DefaultValue[Provider] settings.

#877
What do you hear by "but a value that is consistent with the mock's"?
Because in my test case if the return is a list it's return null but IEnumerable return an empty list,
And for me it's not consistent

[stakx]

What do you hear by [...]

As per my last post, please ignore my initial statement, I was mistaken.

As to your unit tests, your tests fail due to two basic misunderstandings on your part:

• The DateTime test fails because the method you're setting up accepts a DateTimeOffset. While you are passing in DateTime.Now, that gets implicitly converted to DateTimeOffset by DateTimeOffset's implicit operator DateTimeOffset(DateTime). That's why your setup doesn't apply, a DateTimeOffset doesn't fulfill the It.IsAny<DateTime>() criterion.

• You may expect a null return value when calling a mocked method with a return type of IEnumerable<>, but Moq's DefaultValue.Empty strategy generates empty enumerables for such return types. That's been like that for many years now.

  If you want Moq to produce null for such methods, you can hook up a different DefaultValueProvider:

  private class ZeroDefaultValueProvider : DefaultValueProvider
  {
      protected override object GetDefaultValue(Type type, Mock mock)
      {
          return type.IsValueType ? Activator.CreateInstance(type) : null;
      }
  }
  
  var mock = new Mock<T> { DefaultValueProvider = new ZeroDefaultValueProvider() };
  ...

[michelcedric]

var serviceMock = new Mock<IMeteringDataServiceAgent>();
serviceMock.Setup(s => s.GetDataList(It.IsAny<DateTime>())).Returns(_data);
var result3 = serviceMock.Object.GetDataList(new DateTime(2019,1,1));

//Expected the list but received null
//Because during the setup I put It.IsAny<DateTime>() and not It.IsAny<DateTimeOffset>()
Assert.AreEqual(_data, result3);

This unit test fail but in the setup I put DateTime and also during the invocation but it's fail?
It's because in my interface I defined a DateTimeOffset in parameter of GetDataList Method but why return null?
If the setup and invocation use the same type, normally it should work?

[stakx]

Like I already explained above: GetDataList never gets invoked with a DateTime but with a DateTimeOffset, therefore It.IsAny<DateTime>() doesn't match, therefore the whole setup including its Returns verb doesn't apply.

I suggest you read up on user-defined conversion operators and perhaps open up your code in a tool like ILDASM or ILSpy to see for yourself how DateTime.Now gets converted to a DateTimeOffset.

[michelcedric]

Why not raise an exception in this case instead of just return null?
Because Setup with It.IsAny<DateTime>() never working.
Best regards
Thanks

[stakx]

Why not raise an exception in this case [...]?

That is a very valid question, and a good idea! Ideally, such situations would be flagged by a Roslyn analyzer, but since we haven't (yet?) got one for Moq, we could try to produce a runtime error.