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I have a situation where I need to mock some code in production. This is for making one part of code, work in half functionality.

I have to choose to write an empty classes (to implement the interface) , or use a mocking system like moq.

So the question is, do the mocking systems hit the performance, or break some readability of the production code?

update
example:

interface IRocketSystem
{
   void LaunchTheRocket();
}

class SimulationRocketSystem:IRocketSystem
{
...
}

class RocketSystem:IRocketSystem
{
...
}

i found that i have a SimulationRocketSystem classes in production, that small and don't have a lot in the body. the mock system is have one line of code ( new Mock < IRocketSystem >().Object ) to replace classes like this.

the pros for mocking:
 less empty classes in project.

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  • 1
    Can you share some code, or give us more details? Is there only "full functionality" or "half functionality"? Or is it completely configurable? Commented Jul 31, 2009 at 10:06

8 Answers 8

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15

Sounds like a Null Object. I don't believe in using mocking frameworks for this for two reasons.

First, it hurts readability. You implementing the interface with an appropriately named empty class, then you document the intent inside that class. On the other hand, if you use a mocking framework, your documentation needs to be embedded in the code somewhere. Furthermore, it will be confusing as people tend to expect mocks in test code and not understand your intent for using mocks.

Second, you have to consider what happens if someone modifies the interface. What if a method is added? Should it default to returning null - as some frameworks would do? What if the method must return some specific return value according to the interface contract. If you have a concrete implementation, then the compiler will at least protect you somewhat. If you use a mocking framework, you may be out of luck.

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Comments

9

A mock object is something you use for testing, as it will let you assert that it was called correctly. It sounds to me that what you're looking for is more like a stub or a proxy object.

Since you will eventually implement the class in question it would make little sense to have a mock framework do it for you IMO. Why not just create the class and implement it as needed.

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4 Comments

why i need to do something that mocking system making better than me?
I got the impression that the reason the other objects were not present at the moment was because the necessary classes were not implemented yet. If that is indeed the case I would prefer a proxy class because that would allow you to connect the objects in question as needed. I.e. your proxy could forward calls to the real objects when the necessary features become available.
correct, i am using the mock system like system that generating stub object, but have a question, if i can do this in production.
You can do this, but why would you? Since you will eventually implement the necessary classes why not just start by implementing a proxy. If you use stubs from your mocking framework, you'll have to change the code when you start implementing the actual classes.
6

What's wrong with an empty class?

Indeed, it will be replaced with a real class, so you may as well start with a real class.

I think putting mock code of any kind outside tests is a bad policy.

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3 Comments

+1, my preference would be to do the extra bit of work and write my own mock/stub rather than shipping the fake framework just to make it easy to use the stub.
i have a fully implemented class, but sometimes i don't need all functionality (like in example)
"Sometimes I don't ned all functionality" isn't relevant. You have the class, you use it. The point is for production to be completely consistent, not small. Using mocks in production to replace working code is scary.
2

You call it mock, but it seems like what you are doing is just proper separation of concern.

It is a good thing to use polymorphism over if-statements to control what should happen.

Example, say if you want logging to be optional. The imperative approach is to supply a boolean isLogging. Then every time check the boolean like if (isLogging) { ...logging code... }.

But if you instead separate the actual log code as a concern for another object, then you can set that object to one that does what you want. Besides having a null-routed logger that represent logging disabled and one that actually write to a file, it also allow you to supply a logging object that writes to a database instead of a file, it allows you to add features to the logger, such as log-file rotation.

It's simply good object oriented programming.

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2 Comments

yes, but do i need to create an empty classes, or using system that make this easy
I would not use EasyMock to create the empty class. Create the null-routed class (that does nothing in its methods), then inherit it for the logging enabled class and override methods to actually do something. For extra bonus you should use dependency injection.
2

It's perhaps a little unusual, so I would be clear in my comments etc. that this is required functionality. Otherwise someone's going to be very confused as to how test code has made it to production!

As to performance, as ever, you need to measure this since it's so specific. However, I would hazard a guess that as you're mocking functionality you've not written, it may well be much faster than your mocked-out implementation. That's something you may need to educate your users about, since when you provide a final functioning implementation, they could well see a performance hit :-)

The real solution is to provide a dummy implementation to an existing interface, and to provide the real implementation later on.

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1

I don't really know about performance issues. But IMHO, you must be really careful about readability. Isn't it better to declare one or more interfaces and implement it two different ways?

--EDIT

Mocking might be easier, and use less lines of code, but it increases learning curve of your code. If a new guy comes and see your code, he will require more time to understand. Personally, I'd think it is a not yet implemented feature of the code. But if there was another interface implementation, or some other good design decision, I'd "get it" much faster and would feel more secure with changing the code.

Well, that's a personal opinion. Your code will be using a different pattern from what is expected. It's similar to "convention over configuration". If you're not using the convention, you should have a harder time configuring it (in your case, documenting and making clear what you're doing).

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3 Comments

one of implementation is stub class, but in the mock system is one line of code. so personally i thinking about mocking system
@Avram Edited my answer, giving more arguments. It's easier, but IMHO it's more confusing (and therefore less readable)
the new guy must learn unit testing. i am using in testing a lot of mocking.
1

My advice - don't put it in production. Don't ever put anything in production that can slow it down, break it, or otherwise cause you to lose your job :)

But more important than what I think is what is your company policy and what does your manager think? You should never think of making a decision like this on your own - it's called CYA.

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good point, but i am talking about project where i am only the responsible.
doesn't matter - the process is to protect against bad changes, regardless of who is working on the project and who is responsible.
Possibly your manager knows less about whether is this a good decision or not than you. You can go by CYA strategy to not making any decisions up to you, but there are devs whom it is more important to make own decisions in own profession than afraid of some risk of losing a job that probably wont happen.
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I have to choose to write an empty classes, or use a mocking system like moq.

Wrapping it up in a dedicated facade/adapter component and using inner classes should be enough. If your empty classes need to be passed around the system you have a problem.

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1 Comment

No. Passing empty classes is a design pattern.

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