Wednesday, December 08, 2010

Ruby: Why I Prefer Cucumber

I've been struggling to articulate why, in most cases, I prefer high-level integration tests with Cucumber and Webrat (or Capybara) over low-level model, view, and controller tests with RSpec. I think I finally have an example that conveys what I'm trying to say. Consider the following Cucumber test:
Scenario: create a new film unsuccessfully
Given I am logged in as "admin"
And I am on the admin films page

When I follow "New film"
And I press "Create"
Then I should see "There were problems with the following fields:"
And I should see "Name can't be blank"
And I should see "Url name can't be blank"
And I should see "Sort name can't be blank"
And I should see "URL doesn't look like a valid RTMPE URL"
But I should not see "Trailer URL doesn't look like a valid RTMPE URL"
And I should not see "Scene URL doesn't look like a valid RTMPE URL"
This test is short, readable, and easy to write. It doesn't test every possible validation failure, and it's not the only test I have. (In fact, I have some RSpec model tests that test the more esoteric URL validation rules.) However, it does test the model, view, and controller's handling of validation failures, and it even tests that they integrate with each other.

Can you imagine trying to write the same tests by separately testing the model, view, and controller using RSpec? Now, imagine trying to use a separate test for each assertion. That's a lot of code for something so trivial--this ain't rocket science, guys! Finally, remember that when you test the things separately, there's nothing preventing the code from crashing when you put all the pieces together. (For instance, what happens if the controller and view each pass their RSpec tests, but they disagree on the spelling of one of the assigns?)

Is there benefit to testing things separately--absolutely. Is it worth it in this case--absolutely not. I think it's important to remember that at a certain level, our job is to implement features that work. Tests are a means to an end--they help us keep the code working. They don't really have any intrinsic value for the stakeholder. They only have the secondary value of keeping the code working when it is extended.

Just as there is engineering value in implementing features using less code (as long as it remains readable), there is also engineering value in implementing features using less testing code (as long as the tests continue to serve their purpose of preventing regressions).

My point is that Cucumber lets you test more using less effort.


David Aaron Fendley said...

I completely agree. Tests are important, but too much time testing is less time designing. Test smarter not harder.

That being said, I don't really believe in testing views. I can see testing for a few key elements, but views change so rapidly that they aren't worth testing. A redesign can break all of your view tests. In addition, view tests can't give you a feel for the site, its UI, UX, and responsiveness. This is where actual browser-based testing is crucial.

Also, an example such as yours is best left to Rspec. In this case you are actually testing a model and its validations.

Of course, it's just an example, but view testing tends to be a black hole with very little payoff.

Shannon -jj Behrens said...

David, I am not a fan of testing views for the same reasons you mentioned. That's not what Cucumber is really about. It's about testing the whole stack. For instance, an RSpec test for your model's validations can't test that your controller even resulted in a call to validate the model.

Shailen Tuli said...

Your tests do what you want them to, obviously. But why test these things anyway? Presumably you have validation directives in your model and want to confirm that the right error messages are generated. But isn't that really testing Rails internals? If you write custom validation in your model, you should have tests for that (using RSpec). But how much value is there in testing boilerplate validation messages?

Shannon -jj Behrens said...

I'm not checking that Rails is working. I'm checking that validations are actually happening as I think they're happening. It's really easy to type code that you think is working, but is actually failing silently (e.g. this can happen if you misspell a keyword argument). Ruby is especially prone to this. Unless you check that Ruby did the right thing, I don't think you should trust it.