NMock expectations producing weird results - C# Discussion Boards

5-Jun-08 4:09

I am using NMock for creating mock objects. I have found a weird behavior of the expectations set on the object. Here is my code. (This code is just to explain the problem, and not used in production)

public class AccountServices
{
    ICurrencyServices currencyService = null;
    public AccountServices(ICurrencyServices services)
    {
        currencyService = services;
    }

    public string Total()
    {
        return "10" + currencyService.GetTotal();
    }
}

public class CurrencyServices : ICurrencyServices
{
    public string GetTotal()
    {
        return "10";
    }
}

public interface ICurrencyServices
{
    string GetTotal();
}

I am testing Total() method by mocking ICurrencyServices and injecting via constructor to AccountServices. Here goes my test method

[Test]
public void TestTotal()
{
    Mockery mock = new Mockery();
    ICurrencyServices currency = mock.NewMock<icurrencyservices>();
    Expect.Once.On(currency).Method("GetTotal").Will(Return.Value("100"));
    AccountServices services = new AccountServices(currency);
    Assert.AreEqual("10100", services.Total());
}</icurrencyservices>

This works well. But when I add one more assert just down to the last assert

AccountServices services = new AccountServices(currency);
Assert.AreEqual("10100", services.Total());
Assert.AreEqual("10100", services.Total());// This will throw exception

I am getting the following error.

"unexpected invocation of currencyservices.GetTotal()"

. This problem will be solved if I add one more expectation before the last assert. It looks like each time I need to add the expectation before doing anything that calls "GetTotal". Any idea why it works like this ? Why don't the expected value persist until the scope ends ?

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Judah Gabriel Himango5-Jun-08 5:06

Judah Gabriel Himango

5-Jun-08 5:06

Mocks are different than stubs. I'm not familiar with NMock (I use RhinoMocks myself), but the way it works is that

Expect.Once.On(currency).Method("GetTotal")

Set up your expection that GetTotal be called exactly once. Since you did

Assert.AreEqual("10100", services.Total());
Assert.AreEqual("10100", services.Total());// This will throw exception

Calling it 2x is violating the expectation. If that's not what you desired, either change Expect.Once to Expect.Twice (again, not sure of the NMock syntax), or use a stub in place of the mock.

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N a v a n e e t h5-Jun-08 7:04

5-Jun-08 7:04

Thanks for the reply. Problem sorted. Expect.Once was making problem. I changed that to Expect.AtLeastOnce. BTW, what scenarios do you use a stub, and what are it's advantages over mock ?

Thanks again

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Judah Gabriel Himango5-Jun-08 7:13

Judah Gabriel Himango

5-Jun-08 7:13

In short, use stubs for canned results. Use mocks for verifying interactions (e.g. setting expectations). With stubs, it looks just like a real object:

// Stub
myStub.Foo = 5; // Now if anything asks for myStub.Foo, it will return 5. No exceptions thrown, ever.

compared to

// Mock
Expect.Call(myMock.Foo).Return(5); // Exception thrown if myStub.Foo is not called exactly 1 time.

See Martin Fowler's Mocks Aren't Stubs[^] article. MSDN had a good article about the difference between strict mocks, dynamic mocks, and stubs some time ago.

N a v a n e e t h5-Jun-08 7:21

5-Jun-08 7:21

Thanks again. I have very mild usage of NMock, recently started. I have found for mocking interfaces are only used. Say I have a class which needs to be mocked ? Is there a way to go with this ?

Thanks

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Judah Gabriel Himango6-Jun-08 6:45

Judah Gabriel Himango

6-Jun-08 6:45

N a v a n e e t h wrote:
Say I have a class which needs to be mocked ? Is there a way to go with this ?

Partly. Most mock frameworks, such as RhinoMocks, can mock abstract classes and the virtual members of non-sealed classes. Unfortunately, this doesn't work out well because, while C# classes are unsealed by default (good), methods and properties are non-virtual by default (bad). This means most classes you won't be able to mock.

Here at work, we almost always use interfaces. If a class A has a dependency on class B, we change the dependency to be an interface for easy testing and mock injection.

Now, there's one thing you ought to know. There is an extremely powerful mocking framework available -- more powerful than your NMock or my RhinoMocks, called TypeMock.NET. IIRC, TypeMock actually rewrites your IL during the testing phase, allowing you to do anything: mock sealed classes, mock static classes, mock non-virtual methods, mock anything. There's a free community edition available with paid commercial support: TypeMock.com[^]

N a v a n e e t h6-Jun-08 7:37

Suspending a process programmatically, How is that?

6-Jun-08 7:37

Thanks. I will give TypeMock a try. Thanks again

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LordCover5-Jun-08 3:21

Re: Suspending a process programmatically, How is that?

5-Jun-08 3:21

Hello you guys

I'm trying to design a program which can

enumerate a list of processes and you can

suspend a process by clicking RMB (right-mouse button)

and choose Suspend.

I know it is possible, but how?

Note: I tried to use the class Process in .Net framework

but it only has (Start(), Kill()) methods.

LordCover5-Jun-08 3:25

Re: Suspending a process programmatically, How is that?

5-Jun-08 3:25

Oh! I forgot.

I also want to know how to Resume a process after

suspending it.

thanks.

CPallini5-Jun-08 3:29

CPallini

5-Jun-08 3:29

I guess without agreement among processes themselves you can't do that.
Smile | :)

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Re: Suspending a process programmatically, How is that?

LordCover5-Jun-08 3:47

Re: Suspending a process programmatically, How is that?

5-Jun-08 3:47

Ok I know that.

but I want the way to do it.

Anthony Mushrow5-Jun-08 3:33

Anthony Mushrow

5-Jun-08 3:33

There's the ye olde method SuspendThread link[^] and the similar ResumeThread
You can use DllImport to use them, check here[^] for more info on that.

You will also need the process handle for the functions, but you can get that straight out of the process class.

It might not be entirely safe though, strange things could happen, 'specially in some multi-threaded application. Who knows what may happen.

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-SK Genius

Game Programming articles start -here[^]-

Re: Suspending a process programmatically, How is that?

LordCover5-Jun-08 4:50