When to use a Mocking Framework?

Question

So I am playing around with mocking frameworks (Moq) for my unit tests, and was wondering when you should use a mocking framework?

What is the benefit/disadvantage between the following two tests:

public class Tests
{
    [Fact]
    public void TestWithMock()
    {
        // Arrange
        var repo = new Mock<IRepository>();

        var p = new Mock<Person>();
        p.Setup(x => x.Id).Returns(1);
        p.Setup(x => x.Name).Returns("Joe Blow");
        p.Setup(x => x.AkaNames).Returns(new List<string> { "Joey", "Mugs" });
        p.Setup(x => x.AkaNames.Remove(It.IsAny<string>()));

        // Act
        var service = new Service(repo.Object);
        service.RemoveAkaName(p.Object, "Mugs");

        // Assert
        p.Verify(x => x.AkaNames.Remove("Mugs"), Times.Once());
    }

    [Fact]
    public void TestWithoutMock()
    {
        // Arrange
        var repo = new Mock<IRepository>();

        var p = new Person { Id = 1, Name = "Joe Blow", AkaNames = new List<string> { "Joey", "Mugs" } };

        // Act
        var service = new Service(repo.Object);
        service.RemoveAkaName(p, "Mugs");

        // Assert
        Assert.True(p.AkaNames.Count == 1);
        Assert.True(p.AkaNames[0] == "Joey");
    }
}

Answer 1

Use mock objects to truly create a unit test--a test where all dependencies are assumed to function correctly and all you want to know is if the SUT (system under test--a fancy way of saying the class you're testing) works.

The mock objects help to "guarantee" your dependencies function correctly because you create mock versions of those dependencies that produce results you configure. The question then becomes if the one class you're testing behaves as it should when everything else is "working."

Mock objects are particularly critical when you are testing an object with a slow dependency--like a database or a web service. If you were to really hit the database or make the real web service call, your test will take a lot more time to run. That's tolerable when it's only a few extra seconds, but when you have hundreds of tests running in a continuous integration server, that adds up really fast and cripples your automation.

This is what really makes mock objects important--reducing the build-test-deploy cycle time. Making sure your tests run fast is critical to efficient software development.

Answer 2

There are some rules I use writing unit-tests.

1. If my System Under Test (SUT) or Object Under Test has dependencies then I mock them all.
2. If I test a method that returns result then I check result only. If dependencies are passed as parameters of the method they should be mocked. (see 1)
3. If I test 'void' method then verifying mocks is the best option for testing.

There is an old one article by Martin Fowler Mocks Aren't Stubs.

In first test you use Mock and in the second one you use Stub.

Also I see some design issues that lead to your question.

If it is allowed to remove AkaName from AkaNames collection then it is OK to use stub and check state of the person. If you add specific method void RemoveAkaName(string name) into Person class then mocks should be used in order to verify its invocation. And logic of RemoveAkaName should be tested as part of Person class testing.

I would use stub for product and mock for repository for you code.

Answer 3

The mocking framework is used to remove the dependency, so the unit test will focus on the "Unit" to be tested. In your case, the person looks like a simple entity class, there is no need to use Mocking for it.