Mocking Generic Methods With NMock2

  • Article

Recently I was asked how to mock a generic method, now that NMock2 supports generics. Here's how:

Suppose you have this interface:

 public interface IMyInterface

 {

     T DoStuff<T>();

 } 

And this class using IMyInterface:

 public class MyClass

 {

     private IMyInterface mi_;

  

     public MyClass(IMyInterface mi)

     {

         this.mi_ = mi;

     }

  

     public string DoSomething()

     {

         return this.mi_.DoStuff<string>();

     }

 }

Now, you want to write a unit test where you validate that if DoStuff<string> returns Ploeh, MyClass.DoSomething will also return Ploeh. On the version of NMock2 currently installed on my laptop, this is easily done like this:

 [TestMethod]

 public void ValidateDoSomething()

 {

     Mockery mocks = new Mockery();

     IMyInterface mi = mocks.NewMock<IMyInterface>();

     Expect.Once.On(mi).Method("DoStuff").Will(Return.Value("Ploeh"));

  

     MyClass mc = new MyClass(mi);

     string result = mc.DoSomething();

  

     Assert.AreEqual<string>("Ploeh", result);

     mocks.VerifyAllExpectationsHaveBeenMet();

 }

The only thing which is slightly surprising here is that the method name expected is DoStuff, without any indications of generics - I first expected that I should have indicated the method name as DoStuff`1, but apparently, NMock2 doesn't care whether you are expecting a generic or non-generic version of a method (if DoStuff had had a non-generic overload).

Note that this is based on a release candidate of NMock2, so there's no guarantee that this will work exactly identical in the final release.