A bit confused on the differences of Mock frameworks like NMock vs the VS 2011 Fakes Framework.
Going through MSDN, what I understand is that Fakes allow you to mock your dependencies just like RhinoMock or NMock, however the approach is different, Fakes generates code to achive this functionality but Mocks framework does not. So is my understanding correct? Is Fakes just another Mock framework
Your question was about how the MS Fakes framework is different from NMock and it appears the other answers have resolved some of that, but here is some more information regarding how they are the same and how they are different. NMock is also similar to RhinoMocks and Moq, so I'm grouping them in with NMock.
There are 3 major differences I see right off between NMock/RhinoMocks/Moq and the MS Fakes Framework:
The MS fakes framework uses generated code, much like Accessors in prior versions of Visual Studio instead of generic types. When you want to use the fakes framework for a dependency, you add the assembly that contains the dependency to the references of the test project and then right-click on it to generate the test doubles (stubs or shims). Then when you are testing, you are actually using these generated classes instead. NMock uses generics to accomplish the same thing (i.e. IStudentRepository studentRepository = mocks.NewMock<IStudentRepository>()). In my opinion, the MS Fakes framework approach inhibits code navigation and refactoring from within the tests since you are actually working against a generated class, not your real interface.
The MS fakes framework supplies stubs and moles (shims), whereas NMock, RhinoMocks, and Moq all provide stubs and mocks. I really don't understand MS's decision to not include mocks and I am, personally not a fan of moles for reasons described below.
With the MS fakes framework, you supply an alternative implementation of the methods you want to stub. Within these alternate implementations, you can specify the return values and track information about how or if the method was called. With NMock, RhinoMocks and Moq, you generate a mock object and then use that object to specify stubbed return values or to track interactions (whether and how the methods were called). I find the MS fakes approach more complex and less expressive.
To clarify the difference in what the frameworks provide: NMock, RhinoMocks and Moq all provide two types of test doubles (stubs and mocks). The fakes framework provides stubs and moles (they call them shims), and unfortunately does not include mocks. In order to understand the differences and similarities between NMock and MS Fakes, it is helpful to understand what these different types of test doubles are:
Stubs: Stubs are used when you need to provide a values for methods or properties that will be asked of your test doubles by the method under test. For example, when my method under test calls the DoesStudentExist() method of the IStudentRepository test double, I want it to return true.
The idea of stubs in NMock and MS fakes is the same, but with NMock you would do something like this:
Stub.On(mockStudentRepository).Method("DoesStudentExist").Will(Return.Value(true));
And with MSFakes you would do somethign like this:
IStudentRepository studentRepository = new DataAccess.Fakes.StubIStudentRepository() // Generated by Fakes.
{
DoesStudentExistInt32 = (studentId) => { return new Student(); }
};
Notice in the MS Fakes example you create an entirely new implementation for the DoesStudentExist method (Note that it is called DoesStudentExistInt32 because the fakes framework appends the parameter data types to the method names when it generates the stub objects, I think this obscures the clarity of the tests). To be honest the NMock implementation also bugs me because it uses a string to identify the method name. (Forgive me if I've misunderstood how NMock is intended to be used.) This approach really inhibits refactoring and I'd highly recommend RhinoMocks or Moq over NMock for this reason.
Mocks: Mocks are used to verify interaction between your method under test and its dependencies. With NMock, you do this by setting expectations similar to this:
Expect.Once.On(mockStudentRepository).Method("Find").With(123);
This is another reason why I'd prefer RhinoMocks and Moq over NMock, NMock uses the older expectation style whereas RhinoMocks and Moq both support the Arrange/Act/Assert approach where you specify you expected interactions as assertions at the end of the test like this:
stubStudentRepository.AssertWasCalled( x => x.Find(123));
Again, note that RhinoMocks uses a lambda instead of a string to identify the method. The ms fakes framework does not provide mocks at all. This means that in your stubbed out implementations (see the description of stubs above) you have to set variables that you later verify were set correctly. That would look something like this:
bool wasFindCalled = false;
IStudentRepository studentRepository = new DataAccess.Fakes.StubIStudentRepository()
{
DoesStudentExistInt32 = (studentId) =>
{
wasFindCalled = true;
return new Student();
}
};
classUnderTest.MethodUnderTest();
Assert.IsTrue(wasFindCalled);
I find this approach to be a little convoluted since you have to track the call up in the stub and then assert it later in the test. I find the NMock, and especially the RhinoMocks, examples to be more expressive.
Moles (Shims): To be frank, I do not like moles, because of their potential for misuse. One of the things I like so much about unit testing (and TDD in particular) is that testing your code helps you to understand where you have written poor code. This is because testing poorly written code is difficult. This is not true when using moles because moles are actually designed to allow you to test against dependencies that are not injected or to test private methods. They work similarly to stubs, except that you use a ShimsContext like this:
using (ShimsContext.Create())
{
System.Fakes.ShimDateTime.NowGet = () => { return new DateTime(fixedYear, 1, 1); };
}
My worry with shims is that people will start seeing them as "an easier way to unit test" because it doesn't force you to write code the way you should. For a more complete write-up on this concept see this post of mine:
https://jcoop.io/2012/05/21/solid-code-for-solid-reasons/
For more information on some concerns related to the fakes frameworks take a look at these posts:
https://jcoop.io/2012/03/16/38/
If you're interested in learning RhinoMocks here's a Pluralsight training video (full disclosure - I wrote this course and get paid royalties for views, but I think it applies to this discussion so I'm including it here):
http://www.pluralsight.com/training/Courses/TableOfContents/rhinomock-fundamentals
You are correct, but there's more to the story. The most important things to take away from this answer are:
Your architecture should make proper use of stubs and dependency injection, rather than relying on the crutch of Fakes and mocks
Fakes and mocks are useful for testing code you shouldn't or can't change, such as:
Legacy code that does not make use (or efficient use) of stubs
3rd party APIs
Resources for which you have no source code
Shims (known as "Moles", during development) is indeed a mocking framework that operates by way of detouring calls. Instead of painstakingly building a mock (yes, even using Moq is relatively painful!), shims simply use the production code object already in place. Shims simply re-route the call from the production target to the test delegate.
Stubs are generated from interfaces in the target project. The Stub object is just that -- an implementation of the interface. The benefit to using the Stub type is that you can quickly generate a stub without cluttering up your test project with many one-time use stubs, not to mention wasting time creating them. Of course, you should still create concrete stubs, for use across many tests.
Efficiently implementing Fakes (Shims, Mocks and Stub types) takes a little getting used to, but is well worth the effort. I have personally saved weeks of development time, through use of the Shims/Mole, Mocks, and Stub types. I hope you have as much fun with the technology as I have!
As I understand it, the Visual Studio team wanted to avoid competing with the various mock libraries available for .NET. MS often faces hard decisions like this. They are dammed if they don't provide certain functionality ("why doesn't MS provide us with a mock library; mocks are such a common requirement?") and damned if they do ("why is Microsoft acting so aggressively and driving its natural supporters out of the market?") Very often, but not always, they decide to hold back from simply providing their own alternative to available and well-received technologies. That seems to be the case here.
The shim feature of Fakes is really, really useful. Sure, there are dangers. It takes some discipline to ensure you only use this where necessary. However, it fills a big gap. My main complaint is that it is only delivered with the Ultimate edition of VS 2012 and therefore will only be available to a subsection of the .NET development community. What a pity.
Fakes includes two different kinds of "fake" object. The first, called a "stub", is essentially an auto-generated dummy whose default behaviour can (and usually would) be overridden to make it a more interesting mock. It does, however, lack some of the features that most of the currently available mocking frameworks offer. For example, if you want to check that a method on a stub instance was invoked, you would need to add the logic for this yourself. Basically, if you're authoring your own mocks manually now, stubs would probably seem like an improvement. However, if you're already using a more full-featured mocking framework, you might feel like there are some important pieces missing from Fakes stubs.
The other category of object offered by Fakes, called a "shim", exposes a mechanism for replacing behaviour of dependencies that have not been (or cannot be) decoupled adequately for standard replacement via mocks. AFAIK, TypeMock is the only one of the major mocking frameworks that currently offers this sort of functionality.
BTW, if you have tried out Moles before, Fakes is essentially the same thing, finally making its way out of Microsoft Research and into an actual product.
Regarding Fake (Shim + Stub) objects, it has been well defined above, though I guess the last paragraph in the last comment summarizes the whole situation pretty well.
Though a lot of people will argue that Fake (Shim + Stub) objects are good assets to have in some unit testing cases, the downside is that no matter if you're using Visual Studio 2012 or Visual Studio 2013, these options are ONLY available with Premium or Ultimate versions. IOW, this means that you WILL NOT be to run ANY of those Fakes (Shim + Stub) on any Pro version.
You may probably see the Fakes (Shim + Stub) menu option on Pro versions, but beware, there are some pretty strong chances that you will end up with absolutely nothing... It won't generate any compilation error telling you that something important is missing, options are just not there, so don't waste your time...
It's an important factor to consider in a dev team, especially if one is the only one using Ultimate version while everybody else uses Pro version... Moq on the other hand can easily be installed through Nuget no matter which Visual Studio version you use. I had no problem using Moq, the key with any tool is to know what they're used for and how to use them properly ;)
Related
I'm curious as to what method people like to use for mocking and why. The two methods that I know of are using hard coded mock objects and a mocking framework. To demonstrate, I'll outline an example using C#.
Suppose we have an IEmployeeRepository interface with a method called GetEmployeeById.
public interface IEmployeeRepository
{
Employee GetEmployeeById(long id);
}
We can easily create a mock of this:
public class MockEmployeeRepository : IEmployeeRepository
{
public Employee GetEmployeeById(long id)
{
Employee employee = new Employee();
employee.FirstName = "First";
employee.LastName = "Last";
...
return employee;
}
}
Then, in our tests we can explicitly tell our services to use the MockEmployeeRepository, either using a setter or dependency injection. I'm new to mocking frameworks so I'm curious as to why we use them, if we can just do the above?
That's not a Mock, it's a Stub. For stubbing, your example is perfectly acceptable.
From Martin Fowler:
Mocks are what we are talking about here: objects pre-programmed with expectations which form a specification of the calls they are expected to receive.
When you're mocking something, you usually call a "Verify" method.
Look at this for the diff between Mocks and Stubs
http://martinfowler.com/articles/mocksArentStubs.html
I think the choice between writing dummy objects by hand or by using a framework depends a lot upon the types of components that you are testing.
If it is part of the contract for the component under test to communicate with its collaborators following a precise protocol, then instrumented dummy objects ("Mocks") are just the thing to use. It is frequently much easier to test such protocols using a mocking framework than by hand-coding. Consider a component that is required to open a repository, perform some reads and writes in a prescribed order, and then close the repository -- even in the face of an exception. A mocking framework would make it easier to set up all of the necessary tests. Applications related to telecommunications and process control (to pick a couple of random examples) are full of components that need to be tested in this fashion.
On the other hand, many components in general business applications have no particular constraints on how they communicate with their collaborators. Consider a component that performs some kind of analysis of, say, university course loads. The component needs to retrieve instructor, student and course information from a repository. But it does not matter what order it retrieves the data: instructor-student-course, student-course-instructor, all-at-once, or whatever. There is no need to test for and enforce a data access pattern. Indeed, it would likely be harmful to test that pattern as it would be demanding a particular implementation unnecessarily. In this context, simple uninstrumented dummy objects ("Stubs") are adequate and a mocking framework is probably overkill.
I should point out that even when stubbing, a framework can still make your life a lot easier. One doesn't always have the luxury of dictating the signatures of one's collaborators. Imagine unit-testing a component that is required to process data retrieved from a thick interface like IDataReader or ResultSet. Hand-stubbing such interfaces is unpleasant at best -- especially if the component under test only actually uses three of the umpteen methods in the interface.
For me, the projects that have required mocking frameworks were almost invariably of a systems-programming nature (e.g. database or web infrastructure projects, or low-level plumbing in a business application). For applications-programming projects, my experience has been that there were few mocks in sight.
Given that we always strive to hide the messy low-level infrastructure details as much as possible, it would seem that we should aim to have the simple stubs far outnumber the mocks.
Some distinguish between mocks and stubs. A mock object may verify that it has been interacted with in the expected way. A mocking framework can make it easy to generate mocks and stubs.
In your example, you've stubbed out a single method in an interface. Consider an interface with n methods, where n can change over time. A hand-stubbed implementation may require more code and more maintenance.
A mocked interface can have different outputs per test - One test you may have a method return null, another test has the method return an object, another test has the method throw an exception. This is all configured in the unit test, whereas your version would require several hand-written objects.
Psuedocode:
//Unit Test One
MockObject.Expect(m => m.GetData()).Return(null);
//Unit Test Two
MockObject.Expect(m => m.GetData()).Return(new MyClass());
//Unit Test Three
MockObject.Expect(m => m.GetData()).ThrowException();
I tend to write stubs and mocks by hand, first. Then if it can be easily expressed using a mock object framework, I rewrite it so that I have less code to maintain.
I have been writing them by hand. I was having trouble using Moq, but then I read TDD: Introduction to Moq, and I think I get what they say about classical vs. mockist approaches now. I'll be giving Moq another try this evening, and I think understanding the "mockist" approach will give me what I need to make Moq work better for me.
I have read this: http://martinfowler.com/articles/mocksArentStubs.html
My concepts about a stub and a mock are clear. I understand the need of isolation frameworks like moq, rhinomocks and like to create a mock object. As mocks, participate in actual verfication of expectations. But why do we need these frameworks to create stubs. I would rather prefer rolling out a hand created stub and use it in various fixtures.
Have you tried using a library like Rhino Mocks for a day or two before deciding that hand-rolled stubs is a better option?
#chibacity: The whole idea about mocking libraries is to avoid implementations. If I only need to set a single property's value, I don't want to create a whole implementation of an interface. Calling code like
MyObj obj = MockRepository.GenerateStub<MyObj>();
obj.MyProperty = 33;
seems much simpler to me. Not to mention situations where I only need a dumb stub to be passed as a parameter where I don't care what happens to it (so no set up is required).
This doesn't mean you shouldn't roll out your own stubs for more complex scenarios, but in my experience such cases are rare.
My recommendation is to learn how to use a good mocking library (like Rhino) with all its little tricks, my bet is that you'll soon learn to appreciate the reasons for its existence.
Strictly speaking, no, you do not need an isolation framework to create stubs. In fact, Microsoft even has a Stubs Framework that only generates stubs, not mocks.
I've never written an isolation framework myself, but it would seem that it once you have object mocking in place, stubs would be a breeze to create. That might be the main reason that most/all isolation frameworks include stub objects.
In regards to your last sentence ("I would rather prefer rolling out a hand created stub and use it in various fixtures"), have you actually tried that on any sizable project? Sure, maybe you have an interface with a single method that returns a nullable bool -- you only have to write three stubs for that interface, and that's not so bad.
But once you start looking at dozens of interfaces and classes to stub, it simply becomes a mess to keep track of all the different stubs. If you are using each stub in several tests, you can certainly justify hand-writing a stub and putting it aside; but when you only use one particular stub once or twice, it's much easier to keep it as an "anonymous" stub directly generated by the framework, for simplicity's sake.
After using mocking frameworks for a while, I have found that my code design takes on a totally different slant. This slant seems to be directed more in an interaction style. In other words, I become more interested in messages and behavior than state. My objects become services rather than stateful objects as would happen when using stubs. With stubs I end up passing state around to other objects.
The problem for me then becomes more of creating abstraction layers. I have to question whither something should be interacting at certain levels. This helps with creating that 'Last responsible Moment'. So I end up with objects that have producers and consumers. And everything in between is just message channels.
I hope this helps.
I just watched this funny YouTube Video about unit testing (it's Hitler with fake subtitles chewing out his team for not doing good unit tests--skip it if you're humor impaired) where stubs get roundly criticized. But I don't understand what wrong with stubs.
I haven't started using a mocking framework and I haven't started feeling the pain from not using one.
Am I in for a world a hurt sometime down the line, having chosen handwritten stubs and fakes instead of mocks (like Rhinomock etc)? (using Fowler's taxonomy)
What are the considerations for picking between a mock and handwritten stub?
There is nothing wrong with stubs, there is room for stubs, mocks... and spies. All are "test doubles", but with different purposes as explained in Mocks and Stubs aren't Spies:
[...] Before moving on, I'd like to
clarify and define some terms in use
here, which I originally discovered in
Gerard Meszaros' xUnit Patterns
book.
A Dummy Object is a placeholder object passed to the system under test
but never used.
A Test Stub provides the system under test with indirect input
A Test Spy provides a way to verify that the system under test performed
the correct indirect output
A Mock Object provides the system under test with both indirect input
and a way to verify indirect output
[...] And you can let this handy chart
guide your decisions:
PS: Mockito - The New Mock Framework on the Block is worth the read too.
I use the following terminology (introduced by Roy Osherove, the author of the Art of Unit-Testing):
A fake is called a stub if you tell it to fake something in case a method is called with such and such parameters. But if you also verify that such call actually took place or took place exactly N times, then such fake is called a mock. In short. a fake is a stub unless you call Verify() on it and then it's a mock.
Obviously, you will need to use stubs in some cases and mocks in others. So, criticizing stubs roundly is probably wrong and using stubs exclusively is probably wrong as well.
If you haven't started using a mocking framework (alternative term: isolation framework), you should keep an eye on them and reevaluate your options frequently. I went from manual mocks to NMock2 to Moq very quickly. Here's an interesting poll of programmers that shows what they use. Manual mocks/stubs are in the minority, but aren't that uncommon.
Mocks are just a lot easier to throw in. They are a real instance of your class, pre-stubbed with the ability to override the action of any method with minimal boilerplate.
There are lots of little considerations such as: If you don't want to deal with any of the methods, you can either have it act as a no-op or fail the test--your choice--but either way virtually no code.
How much boilerplate do you get when you stub out a class? How do you handle it if your class is final? Do you play tricks to get your stub on the classpath first, or do you use different source?
I recommend just starting with the mocks--It's easier all around.
There is nothing wrong with using stubs instead of mocks.
If you want to get technical, mocks are "smart" objects with expectations that can be verified. Stubs are dummy objects that return preset values. See Mocks Aren't Stubs.
But many people (myself included) prefer to do state testing with stubs rather than behavior testing with mocks. You inject a stub into the class under test, you call a method, then you check the state of the class under test. It tends to make for less brittle tests than asserting that the class's internals called method X of a mock object with argument Y.
I don't think you're in for a world of hurt. If you haven't started feeling the pain, you probably don't need an isolation/mocking framework yet. When and if you do, having handwritten stubs/fakes around isn't going to hurt anything.
If you have a lot of interfaces, or if your interfaces have a lot of methods, an isolation/mocking framework can save a lot of time over hand-coding stubs.
I like Moq a lot; I find it easier to use than Rhino Mocks for creating stubs.
Mocks and stubs is used to achieve a real unit test. You just mock all the dependencies, and unit test your class in isolation.
I'm currently using MOQ for mocking and stubbing.
Recently there has been quite some hype around all the different mocking frameworks in the .NET world. I still haven't quite grasped what is so great about them. It doesn't seem to be to hard to write the mocking objects I need myself. Especially with the help of Visual Studio I quickly can write a class that implements the interface I want to mock (it auto-generates almost everything for me) and then write an implementation for the method(s) I need for my test. Done! Why going through the hassle of understanding a mocking framework for the sole purpose of saving a few lines of code. Or is a mocking framework not only about saving lines of code?
Once I finally got the hang of mock objects, I realized that they're essential for unit testing for the same reason that double blind testing or control groups are essential for scientific trials: they isolate what you're actually testing.
If you're testing a class which has quite a bit of interaction via other interfaces, you not only save the lines of code on having to mock each and every interface, but you also gain the ability to do things like "throw an exception if an unexpected method is called" or "exception if these methods are called out of order". You can get remarkably sophisticated with mock frameworks, and though I'll quickly admit there's a large learning curve, when you get up to speed they'll help make your unit tests more thorough without being bloated.
You actually identified one of the key points of a mock framework in your question. The fact that you code the mocks yourself is not something the developer should be concerned with. The mocking frameworks give you implementations of interfaces programatically, plus they are functional (based on your setup of the mock).
What do you do if you are testing an ICustomerDAO, for example, and you want to test some method 14 times each with different outcomes? Implement 14 different classes manually? I doubt that anyone would want to do that.
Mocks give you the power to define what will happen with parts of your classes when you are not concerned with whether or not they will actually work, like throwing exceptions whenever you want them to, returning zero results and making sure you handle that correctly, etc...
They are a great unit testing tool.
Previous questions that may help:
What is a mock and when should you use it?
Mockist vs classical TDD
I find that using a mocking framework allows me to generate tests a lot faster and with better verification that what I expect to happen in the test actually is happengin. I have in the past implemented stubs or fakes myself. I found that I needed to generate stubs specific to the test that I wanted and this took a lot of time. I can create the same test much faster using a mocking framework. The good ones support the generation of fakes, stubs or mocks with straightforward syntax.
It takes a while to get the hang of it, I avoided it for a while but now wouldn't try to work without a mocking framework for the reasons #Chamelaeon states.
Roy Osherove had a poll about Mock Frameworks and down in the comment section, there is a discussion (albeit brief) about whether one needs a Mock Framework or not.
I personally have been manually doing exactly as you stated and it has worked well enough, but this has mainly been out of habit rather than a closely-held opinion on mock frameworks in general.
Well I certainly don't think that you NEED a mocking framework. It's a framework like any other, and it's ultimately designed to save you some time and effort. You can also do things like roll your own common data structures like stacks and queues, but isn't it generally easier to just use the ones built into the class libraries that ship with the compiler/IDE of your language of choice?
I'm sure there are other compelling reasons for using mocking frameworks, though I'd leave it to the TDD and unit testing gurus to answer.
For the same reason you wouldn't try to write unit tests without NUnit. A mocking framework will assist you in verifying state and behavior over hundreds of unit tests. It's worth the 2 weeks or so of pain to get up to speed and really helps you focus on what needs to be tested.
One thing that troubles me about a mocking framework is that "what a function should o/p given an i/p" via
when(mock.someMethod("some arg")).thenReturn("something");
statement is spread across many unit test classes.
Let me elaborate with an example. Lets say there was a DAO Interface function getEmp(int EmpID) which was returning an Employee Object when passed an Employee ID as a parameter. Assume that this function was being mocked by 10 different unit test classes. Now if in the future, this function were changed to return a newer version of the Employee Object, one would have to go to each of the 10 different classes to update this change.
The disadvantages are as follows...
a) I don't know how to figure out all the classes which mock this function so that I can go update this change.
b) My existing test cases which consumes the mock DAO object continue to be blissfully unaware of the changes that have happened to the DAO Interface because the mock has not changed and hence continue to be green.
Ideally, if I were to have coded a single mock class myself and consumed it everywhere, I would have just one place to update for the newer version of the Employee object. Also, once I update at this one place, all my existing test cases which consume the mock would break and I would then know exactly what places I need to go and do an update for the new Employee Object.
Any thoughts on my views..
One of the good things about a mocking framework is that it allows setting expectations on the objects being mocked. With the expectations I can then set up all sorts of conditions to exercise the code thats being tested.
An isolation framework or mocking framework allows you to test the code you want, without its dependencies. It makes for short running tests, allows you to debug quickly, and easily build a safety net of tests around the code. Different frameworks have different features, and as said before - it's a tool, and you should select the right tool for the job.
I've use rhino mocks for a mocking framework. I and 5 other developers used it on a large enterprise application that was an 8 month project. We used tdd on the project. Was it worth it? I guess. Was there such a massive huge selling point to using mocks that I have to use it on every project? In my opinion, no. It is not something that is necessary, it is just a tool that you can use if you want to try it out. Some projects you can roll out your own mock classes as some here say they prefer - it is easier. Other projects are larger and may require a mocking framework. The key word (in my opinion) is MAY require... how much code coverage do you require? To me, that is another consideration to using mocks. The project I did with tdd/rhino mocks we were required to have 80% code coverage so the mocks helped us attain that. If our code coverage requirements were less, for example 40%, we probably would have not used a mocking framework and just wrote our own mock classes as others mention they do.
I am curious about how many of you folks incorporate mocking of objects (frameworks like JMock, NMock, RhinoMocks hand in hand with unit testing frameworks) into your daily development process. What are your experiences?
You see, I develop on top of a GIS (geographic information systems) platform, in which most of work pertains to some way of handling data. As its data object model is quite complex (many many classes and interfaces, all COM-based), it is also quite difficult and cumbersome to mock. In this case, mocking incurs a great deal of overhead when writing test suites. I wonder if there are people in similar situation, or just, how does mocking (in whatever situation you are in) work for you.
On a recent project that I worked on we used mock objects extensively in our unit testing approach. The project was 100% Java and moderately sized (about 100,000 lines of non-commented code). It was a Swing-based desktop application - and the only effective way that we found to test the user interface logic was through an MVC variant design that allowed us to use mock objects to substitute for the actual Swing user interface classes for the automated testing. We also used mocking extensively in the testing of our data access layer (Hibernate/DAOs).
In the user inteface use, the Mocks were easy and straightforward to build. And the design of the application (Fowler Passive View) easily incorporated mocks. This was not the case for the mocks used in testing the data access layer. But I can say that it was clearly worth the effort. In fact, most of the 'effort' really focused on coming up with a reusable solution that minimized the work that a developer had to do to create each individual mock. I'd recommend taking the time to dig into and discover an approach for your situation that allows you to easily mock up your GIS data layer. That - or just manually mock up each class. Either way the ability to run the automated unit tests that rely on the mocks is worthwhile...
In my situation mocks work really nice. But I'm using Python, which is so dynamic that it makes many things involving testing much, much easier.
In situation like yours, when application is mainly data-driven (as far as I see), mocks may not be as useful. Just passing data in and watching it come out should be enough for testing. I would just make sure that application is modularized enough, so this approach can be applied to reasonably small components.
Mocking can be useful in some kind of project. But, sometimes mocking is very time consuming and the ROI of it is low.
Trying to test Sharepoint it seems that mocking is the only way, and only typemock will let you mock sealed classes.
Mocking is used very extensively in my case. Mocks are usually for the classes that has external dependencies, e.g. network, database, filesystem. Any of these can introduce flakiness in the tests if mocks are not used.
If the mocks that you find costly to write because there are a lot of fake data to populate, you could set some pre-populated data objects as constants and use them or slightly modified copies in your test. If such data objects has external dependencies, then maybe refactor it in a way you can separate the two concerns.
There is an initiative started by Dave Bouman to try and build a community library of Mocks for use in ArcObjects related unit testing. His blog and this svn repository have great information related to unit testing GIS systems
http://blog.davebouwman.net/CategoryView,category,Unit%2BTesting.aspx
http://svn2.assembla.com/svn/arcdeveloper/TestingUtilities/trunk/