Mathias Meyer
Mathias Meyer


Pat Maddox recently published a blog post on mocking called “You Probably Don’t Get Mocks.” I wanted to write something on my experiences with mocks for a while now, so here’s good reason to finally do so. I’m a recovering mock addict, if you will, so this is my retribution of things I learned over the last 18 months, and how my testing workflow changed with them.

When you dive into RSpec, mocking will be put in your face right from the start. For some it might even be the thing that makes BDD what it is, testing how your code behaves. I followed that path for about a year. I wouldn’t say religiously, but I did use it wherever it made sense. The project started out with no tests at all, so mocking actually did come in handy for some of the bigger controllers, in the beginning, that is. It also made the whole test suite rather speedy. When I was finished with the project, it had about 2200 specs which took less than two minutes. A good run still, certainly with room to improve performance.

But towards the end some things changed, my testing workflow changed. Pat might argue that I probably don’t get mocks, but the tests felt brittle. That’s not all the mocks’ fault, the code still was very brittle in some areas, so the tests had to do quite a lot to get a decent setup. It just didn’t feel right to use mocks for controller tests.

These days I use Cucumber to do full-stack testing, so for one I agree with Pat. If you have a decent acceptance test suite, the brittleness mocks and stubs bring into your code gets less annoying. But in all that got me thinking. If I need integration tests to secure that my mocks still do what they’re supposed to, something isn’t right. On said project I only had a good suite of controller and unit tests (yeah, their specs, I know, I’m not religious about the name, in the end they all test the code), so I had to rely on the tests to give good and reliable results, at least on that level.

Write Code That Doesn’t Suck

When I watched Yehuda Katz’ talk at RubyConf 2008, it hit me. Who cares what your controller does on the inside, how it get things done? Does it really matter? Is that a defined business value? No, because what matters is what comes out in the end, what the user sees. I also watched the talk called “Testing Heresies” that Pat mentions, but here I agree with Pat, it was not at all convincing. But for me, Yehuda’s talk hit right home.

It pretty much was that realization that made me testing framework agnostic. It just doesn’t matter to me what you’re using to write tests, as long as you write them, and as long as they’re a reliable base for working with your code. Sure I appreciate RSpec’s syntax and it trying to embrace BDD to the fullest, but in the end, it just doesn’t matter. If you don’t care about all the glory internal details of a test, then it doesn’t matter if you use a fancy should syntax or plain old Test::Unit tests.

With Cucumber, the question for me is: If I have a decent acceptance test suite, then what do I need to do big testing on the controller level for? The acceptance test suite should cover most of what the controller does anyway. I started using resource_controller a while ago, and it takes away a lot of the “complexity” you usually have in your controllers. It reduces the controllers to what models in the Java world used to be: Dumb classes, and therefore reduces the amount of testing code for controllers. While that feels right to me, you could still argue that mocks and stubs make sense to test those cases where you still write tests on the controller level. Sure, but even in these cases I’d rather rely on real data, even if that’ll slow down my test suite. The slowdown can’t be that bad, if it is, then your controllers are simply doing too much.

Mocks Don’t Fix Slow Tests

Jon Dahl recently posted a post on slow tests being a bug. Interestingly he didn’t mention mocks or stubs as a measure to speed up tests. Maybe he forgot, but to me that’s pretty interesting. It used to be an compelling reason to use mocks for me, but these days I’d rather have a slower test suite, but one that’s more reliable. Using mocks to speed up your tests is just wrong, you exchange reliability for speed. Call me paranoid, but that doesn’t seem right to me.

The isolation of controller and model for me just is a no-brainer. Whether you like it or not, the controller doesn’t work without the model. Even stubbing out the model doesn’t hide that fact. I embrace it, and by keeping my controller as small as possible, using a tiny abstraction like resource_controller and factories for test data, I just don’t care about using mocks anymore. It gives me a much better sense of safety. If you get mocks or not, that’s what it boils down to. If you feel like mocks give you a false sense of security, stop using them, if you’re comfortable with them, for the love of BDD, keep using them, but don’t expect me to use them when I’m writing tests.

All that said, there is still one good reason to use mocks and stubs for me. It’s to stub out external services. So yeah, if you want to say that I probably don’t get mocks, feel free. Personally I just feel a lot more comfortable without them, and to me that’s way more important. Keep your controller tests as small as possible, and the whole reasoning for mocks and stubs vanishes. Mocks dumb down your tests, and that’s exactly what should not happen under any circumstances. If anything needs to know all the facts about a piece of code under test, it should be the tests themselves.