Consider this part of an occasional series where I attempt to revisit tools discussed in Rails Test Prescriptions that have undergone some revision. (NOTE: Most of this was written before the DHH Twitter-storm about testing this week. For the purposes of this post, I’m choosing to pretend the whole thing didn’t happen.)
The cucumber-rails gem released version 0.4 last week, which had some significant changes, and intensified what we might call the opinionated nature of Cucumber over what a Cucumber scenario should look like.
If you update cucumber-rails, you need to re-run the
rails generate cucumber:install to see the new stuff.
There are a couple of minor changes – the default env.rb file is much simpler, the capybara date selector steps now work with Rails 3, that kind of thing. The biggest change, though is conceptual, and comes in two parts.
Part one is best laid out by the new first line of the web_steps.rb file:
TL;DR: YOU SHOULD DELETE THIS FILE
The header goes on to say that if you make use of these steps you will end up with verbose and brittle cucumber features. Also, your hair will fall out, and you will have seven years bad luck. The last may be more implied than stated.
Why would they do such a thing? And what’s the “official” preferred way to use Cucumber now?
Well, it’s not like the Cucumber dev team has me on speed-dial or anything like that, but since they subtly included in the web_steps.rb file links to, count ‘em, three separate blog posts explaining how to best use Cucumber, I will follow that subtle, yet blazing, trail and try to put it together in some coherent way so that I can understand it.
(Note to Cucumber dev team: if you feel the need to link to this post in future versions of Cucumber, you should consider yourself as having permission to do so….)
Anyway, the Cucumber team is making a very opinionated statement about how to use Cucumber “with the grain”, and I actually don’t think that statement is “don’t use the web_steps” file – I think that some parts of the web_steps file have a place in the Cucumber world.
Here’s the statement as I see it:
A Cucumber scenario is an acceptance test.
As such, the scenario should completely be in the domain of the user.
A Cucumber scenario should not have any reference to implementation details.
Implementation details include, but are not limited to: CSS selectors, class names, attribute names, and HTML display text.
As a good rule of thumb, if you are putting something in your Cucumber steps in quotation marks, you should at least think about whether your Cucumber scenario is at a high enough level. In the Cucumber world, the place for implementation-specific details is in the step definition files. If the acceptance criteria changes, the scenario should change, but if the implementation changes, only the step definitions should change.
This sharp separation between the acceptance test and the implementation is a feature, not a bug, in Cucumber (By the way, you do not want bugs in your cucumbers. Yuck.) The separation is what makes Cucumber a true black-box test of your application, and not a black box riddled with holes.
That said, full-stack testing that is based on knowing implementation details – which is “integration testing” rather than “acceptance testing” – is a perfectly valid thing to do, especially in a case where there isn’t an external customer that needs or wants to see the acceptance testing. But, if you are actually doing integration testing, then you don’t need the extra level of indirection that Cucumber offers – you should drop down to Steak, or Rails integration tests, or the new Capybara acceptance test DSL or something.
Okay, so. Acceptance testing is not integration testing, and if you are trying to do integration testing via Cucumber, you will be frustrated, because that’s not what Cucumber is good at. To me, there’s a value in acceptance testing, or in this case, acceptance test driven development, because it’s helpful to try and describe the desired system behavior without any implementation details confusing the issue.
Which brings us back to the question of how you actually replace the web steps in your Cucumber scenarios. Essentially the idea is to replace implementation-based steps with steps that describe behavior more generically. You might have something like this:
Scenario: Updating a user profile Given a user named "Noel" with a preference for "Cool Stuff" When I go to the edit profile page And I fill in "bananas" for "Favorite Food" And I select "Comic Books" from "Preferences" And I press "Submit" Then I should see "Bananas" And I should see "Comic Books"
That’s not horrible, because it doesn’t have any explicit CSS or code in it, but it’s still very much about implementation details, such as the exact starting state of the user, the labels in the form, and the details of the output. On the plus side, the only step definition you’d need to write for this is for the first step, every other step is covered by an existing web step. But… I’ve written my share of Cucumber scenarios that look like this, and it’s not the best way to go. It’s hard to tell from this step what the most important parts are and what system behavior is actually being described.
The implicit version of the scenario looks more like this:
Scenario: Updating a user profile Given I am an existing user with a partially completed profile When I go to edit my profile And I fill in new preferences Then I see my new preferences on my profile page
Two questions to answer: why is this better, and how does it work?
The second question first. We need to write step definitions for all these steps. Normally, I write these in terms of the underlying Capybara or Webrat API rather than calling web steps. The second step doesn’t need a full definition, it just needs an entry for /edit my profile/ in the paths.rb file (right now, it seems like that’s about the only step in the web steps file that the Cucumber team is willing to use), but the other three steps need definitions – here’s what they might look like, this might have a typo or syntax jumble, it’s just the basic idea.
Given /^I am an existing user with a partially completed profile$/ do @user = Factory(:user) @user.profile = Factory(:profile, :preference =\> "Cool Stuff", :favorite\_food =\> nil) end When /^I fill in new preferences$/ do fill\_in("Favorite Food", :with =\> "Bananas") select("Comic Books", :from =\> "Preferences") click\_button("Submit") end Then /^I see my new preferences on my profile page$/ with\_scope("preference listing") do page.should have\_selector(selector\_for("bananas are my favorite food")) page.should have\_selector(selector\_for("comic books are my preference")) end end
If you are used to Cucumber but haven’t used the 0.4 Rails version yet, the last step will look unfamiliar. Bear with me for a second.
Why is the second version better? It’s not because it’s shorter – it’s a bit longer, although only a bit (the first version would need a step definition for the user step as well). However, the length is split into more manageable chunks. The Cucumber scenario is shorter, and more to the point, each step is more descriptive in terms of what it does and how it fits into the overall scenario. The new step definitions you need to write add a little complexity, but not very much, and my Cucumber experience is that the at this size, the complexity of the step definitions is rarely the bottleneck. (For the record, the bottleneck is usually getting the object environment set up, followed by the inevitable point of intersection with implementation details, which is why I’m so keen to try and minimize intersection with the implementation.)
Yes, the scenario is something you could show a non-developer member of the team, but I also think it’s easier for coders to comprehend, at least in terms of getting across the goals of the system. And this is supposed to be an acceptance test – making the goals of the system explicit is the whole point.
Okay, either you believe me at this point or you don’t. I suspect that some of you look at the step definitions and say “hey, I could string those seven lines of code together and call it a test all by itself”. Again, if that’s what works for you, fine. Any full-stack testing is probably better than no full-task setting. Try it once, though. For me.
Back to the step definitions, the last one uses the
selector_for method – and I hope I’m using it right here because I haven’t gotten a chance to work with it yet, and the docs aren’t totally clear to me. The idea behind
selector_for is to be analogous to the
path_to method, but instead of being a big long case statement that turns a natural language phrase into a path, it’s a big long case statement that turns a natural language phrase into a CSS selector. The big lng case statement is in the support folder in a selectors.rb file. The
with_scope method uses the same big case statement to narrow the statements inside the block to DOM elements within the snippet.
As with the paths, the idea is to take information that is implementation specific and likely to be duplicated and quarantine it into one particular location. As I said, I haven’t really incorporated this into my Cucumber routine yet, my first thought is that it’ll be nice to hide some of the complex CSS selectors I use in view testing, but I worry that the selectors.rb file will become a mess and that there’s less probability of duplicating a snippet.
I sure wish I had a rousing conclusion to reward you as this post nears the 1750 word mark. I like the direction that these changes are taking Cucumber, they are in line with what I’ve found to be the best use of the tool. Take a chance and try writing tests as implicitly as you can, as an exercise and see if it works for you.