Using Moq and TDD, where to start?

Question

I have a server application and I was wondering where I should start if I want to start implementing TDD and using Moq.

What good books I could read on the subject, which aren't too "web-oriented"?

I have questions on the matter, like:

Should I mock every object I want to test, or only those which I can't implement, like text writers?

My server needs a lot of setup before it can actually do anything I want to test, should I just cram that into a [TestInitialize] function?

How should I chain my tests, if I want to test deeper functionality?

Answer 1

You don't mock the objects you want to test. If you do that, you're testing the mock, not your object! You need to mock the dependencies of the objects you're testing.

Answer 2

I recommend two books: Test Driven Development by Example, by Kent Beck. It's an excellent book on TDD, which I particularly enjoy because he walks through an example, which is very useful in getting a sense for the rhythm and thought process. On the other hand, it's a bit light on mocking. For that I would read The Art of Unit Testing, by Roy Osherove. As the title suggests, it's not focused on TDD specifically, but rather on how to write good unit tests; he has a good coverage on mocks and stubs.

Regarding what you should mock, the idea of mocking is to allow you to isolate the class/function you are testing from the rest of the environment, so that you can test its behavior against a fake environment you control. In that frame, you should not be mocking the class, but rather things it depends upon.

A trivial example: if you had a class using a Logger, testing that the class "writes" to the logger would be very painful, and could involve things like checking whether the logger has written in a text file. This is not a good idea on lots of levels - starting with the fact that your class doesn't care about how the logger does its job specifically. In that case you would replace the Logger instance in your class with a Fake, mocked Logger, and you can then verify that your class is calling the Logger at appropriate times, without worrying about what the logger does, exactly.

Regarding server initialization: a unit test is typically in memory, with no dependencies to the environment, so if you are doing TDD, you should probably not have to do that. In general, too much (any?) initialization code in a unit test is a bad sign.

This suggests that you are looking more for acceptance tests / BDD style tests. I recomment this recent article in MSDN Magazine on Behavior-Driven Development with SpecFlow and WatiN; it explains how you can develop in a test-first manner by developing together high-level tests which verify that the application is doing what the user wants (acceptance tests, where you would run your actual server and app), and that it's doing it by having small pieces of code that do what the developer intends (unit tests).

Hope this helps, and happy testing!