Is object mocking used extensively?

Question

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.

Answer 1

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.

Answer 2

Mocking can be useful in some kind of project. But, sometimes mocking is very time consuming and the ROI of it is low.

Answer 3

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...

Answer 4

Trying to test Sharepoint it seems that mocking is the only way, and only typemock will let you mock sealed classes.

Answer 5

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.

Answer 6

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/