How to correctly mock a property of a mocked class?

Question

I was reviewing some unit tests from a colleague, and I saw something in the lines of:

var dogMock = new Mock<Dog>();

dogMock.Setup(d => d.Bark(It.IsAny<Volume>())).Returns(someMockedBarking);
dogMock.Object.Age = 2;

Is it ok that a property of the Object is directly set, or is it better to use the Setup and Returns like the following?

dogMock.Setup(d => d.Age).Returns(2);

In both cases, the unit tests succeeds though.

Answer 1

It depends on your needs. Note that the first one requires SetupProperty or SetupAllProperties to work correctly (docs):

var mock = new Mock<IFoo>();
// mock.SetupProperty(f => f.Name);
// mock.SetupAllProperties();
IFoo foo = mock.Object;

foo.Name = "bar";
Assert.AreEqual("bar", foo.Name); // Throws if both commented out

public interface IFoo
{
    string Name { get; set; }
}

Also in some cases the SetupProperty approach can have advantages due it's "tracking" behavior - if the mocked dependency has it's property heavily manipulated (multiple gets and sets are performed) it will allow easier setup and behaviour closer to "black box".