CODEWITHSUNDEEP
rhino-mocks
ddm
ddm

Reputation: 488

Rhino mock a singleton class

I want to test my controller that depends on a hardware C# class, not an interface.

It's configured as a singleton and I just can't figure out how to RhinoMock it.

The hardware metadata (example) for the dependent class:

namespace Hardware.Client.Api
{
    public class CHardwareManager
    {
    public static CHardwareManager GetInstance();
    public string Connect(string clientId);
    }
}

and in my code I want this something like this to return true, else I get an exception

if( !CHardwareManager.GetInstance().Connect("foo") )

I mock it using:

CHardwareManager mockHardwareMgr MockRepository.GenerateMock<CHardwareManager>();

But the Connect needs a GetInstance and the only combination I can get to "compile" is

mockHardwareMgr.Expect    (x => x.Connected ).Return(true).Repeat.Any();

but it doesn't correctly mock, it throws an exception

but this complains about typing the GetInstance

mockHardwareMgr.Expect (x => x.GetInstance().Connected).Return(true).Repeat.Any();

So my problem - I think - is mocking a singleton. Then I have no idea how to make my controller use this mock since I don't pass the mock into the controller. It's a resource and namespace.

90% of my work requires external components I need to mock, most times I don't write the classes or interfaces, and I'm struggling to get them mocked and my code tested.

Any pointers would be welcome.

Thanks in advance (yes, I've been searching through SO and have not seen something like this. But then, maybe my search was not good.

Upvotes: 0

Views: 787

Answers (2)

No answer
No answer

Reputation: 935

As Igor said RhinoMocks (and most other free mocking frameworks, e.g. Moq) can only mock interfaces.

For mocking classes try (and pay) TypeMock.

For mocking singletons see my answer to: How to Mock a Static Singleton?

Yes, I'm somewhat undermining the common understanding of what's deemed testable and thus "good" code. However I'm starting to resent answers like "You're doing it wrong. Make everything anew." for those answers don't solve the problem at hand.

No, this is not pointing at Igor, but at many others in similar threads, who answered "Singletons are unmockable. (Make everything anew.)".

Upvotes: 0

Igor Brejc
Igor Brejc

Reputation: 19004

The usual way to avoid problems with mocking external components is not to use them directly in your code. Instead, define an anti-corruption layer (usually through an interface that looks like your external component) and test your code using mocked implementation of this interface. After all, you're testing your own code, not the external one.

Even better way is to adjust this interface to your needs so it only exposes stuff that you actually need, not the whole API the external component provides (so it's actually an Adapter pattern).

External components are tested using different approaches: system testing, in which case you don't really mock them, you use the actual implementation.

Usually when you try to get Rhino Mocks to do something which feels unnatural and Rhino growls, this is a good sign that your approach is not the right one. Almost everything can be done using simple interface mocking.

Upvotes: 1

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