MoQ Mocks – Use virtual method or interfaces?

I’ve switched over and am using MoQ full time now on my projects and LOVE it.  The lambda expressions may seem strange to others, but I like that I can read my code, left to right, and it’s almost verbatium to what I want to do.

The one snafu that really bugs me is when testing classes that are based off of a base class rather than an interface.  For example, my LINQ business layers fall back onto a prototype over on the MSFT Code Gallery and the Microsoft Dynamic Query libraries (which is part of the VS2008 samples, just add the class file into your project).

Unfortunately, the base class library has everything has static methods.  That’s no good for testing.  However, that’s not enough.  I kept getting the following error:

System.ArgumentException: Invalid expectation on a non-overridable member.

Say huh?  Non-overridable?  Why’s it trying to override the method?

I finally found the answer over on the MoQ Google Groups—”[Castle] DynamicProxy can not intercept methods calls to non virtual, non abstract methods”.

Daniel Cazzulino goes on to explain:

it’s a limitation of the CLR since its inception: there’s no built-in
interception mechanism.

so, the interception mechanism we use is auto-generated classes that inherit from the types to mock, and override all members to provide the interception. that’s why they need to be virtual.

we’re reusing the interception library from Castle DynamicProxy for doing that.

Well, that explains that, but I’m not sure I like decorating my classes simply to enable mocking. 

public virtual bool Add(int studentId, string enteredBy) { }

The mock and test then look like:

[TestMethod]

public void Reports_AddReport()

{

       var mock = new Mock<ReportsController>();

       mock.Expect(x => x.Add(studentId, enteredBy)).Returns(true);

      

       Assert.IsTrue(mock.Object.Add(studentId, enteredBy));

}

What would be a better solution? 

In my opinion, taking the base class and pushing the members up into an interface, then mocking the interface would be best.

With the methods nicely tucked into a new IReportsController interface and the virtuals banished from our base class, our test only changes slightly, but without opening up the methods in the base class to override.

[TestMethod]

public void Reports_AddReport()

{

       var mock = new Mock<IReportsController>();

       mock.Expect(x => x.Add(studentId, enteredBy)).Returns(true);

      

       Assert.IsTrue(mock.Object.Add(studentId, enteredBy));

}

Are there times where virtual methods would be a better idea?

Tags: Moq, Unit+Testing, Mocks, Dynamic+Query