15 Expert Tips for Using Cucumber

Here we are: the 3rd and final post in my series on Cucumber. Check out the LazyWeb in action: I put out calls for 'Cucumber Best Practices' and received an assortment of responses—thanks to everyone who contributed! After collecting and reviewing all the responses, I've come up with a list of 15 expert tips you want to keep in mind when working with Cucumber.

In retrospect, I don't really like the term Best Practice—the value of most practices is very much context dependent. That said, some ways of doing things are just generally better than others, so here are some of those good things to keep in mind. I'll comment briefly on each one.

1. Feature Files Should Actually be Features, Not Entire Portions of an App

One feature per well named file, please, and keep the features focused.

2. Avoid Inconsistencies with Domain Language

You'll get the most benefit out of using Cucumber when your customers are involved. To that end, make sure you use their domain language when you write stories. The best course of action is to have them involved in writing the stories.

3. Organize Your Features and Scenarios with the Same Thought You Give to Organizing Your Code

One useful way to organize things is by how fast they run. Use 2-3 levels of granularity for this:

  • Fast: scenarios that run very fast, e.g. under 1/10 of a second
  • Slow: scenarios that are slower but not painfully so, maybe under one second each
  • Glacial: scenarios that take a really long time to run

You can do this separation several different ways (and even some combination):

  • Put them in separate features
  • Put them in separate subdirectories
  • Tag them

4. Use Tags

Tags are a great way to organize your features and scenarios in non functional ways. You could use @small, @medium and @large, or maybe @hare, @tortoise, and @sloth. Using tags let you keep a feature's scenarios together structurally, but run them separately. It also makes it easy to move features/scenarios between groups, and to have a given feature's scenarios split between groups.

The advantage of separating them this way is that you can selectively run scenarios at different times and/or frequencies, i.e. run faster scenarios more often, or run really big/slow scenarios overnight on a schedule.

Tagging has uses beyond separating scenarios into groups based on how fast they are:

  • When they should be run: on @checkin, @hourly, @daily
  • What external dependencies they have: @local, @database, @network
  • Level: @functional, @system, @smoke
  • Etc.

5. Use Rake Tasks to Run Features

This provides a consistent environment for running features: this way each run uses the same set of options and parameters. This goes a long way toward maintaining deterministic results.

Another benefit is that this makes for easy integration with continuous integration tools. There is a single point of entry into the spec run, with all options/parameters encapsulated.

6. Don't Get Carried Away with Backgrounds (Stick to Givens)

The larger the background, the greater the load of understanding for each scenario. Scenarios that contain all the details are self-contained and as such, can be more understandable at a glance.

7. Make Scenarios Independent and Deterministic

There shouldn't be any sort of coupling between scenarios. The main source of such coupling is state that persists between scenarios. This can be accidental, or worse, by design. For example one scenario could step through adding a record to a database, and subsequent scenarios depend on the existence of that record.

This may work, but will create a problem if the order in which scenarios run changes, or they are run in parallel. Scenarios need to be completely independent.

Each time a scenario runs, it should run the same, giving identical results. The purpose of a scenario is to describe how your system works. If you don't have confidence that this is always the case, then it isn't doing its job. If you have non-deterministic scenarios, find out why and fix them.

8. Write Scenarios for the Non-Happy-Path Cases As Well

Happy path tests are easy; edge cases and failure scenarios take more thought and work. Here's where having some good (and yet pathological) testers on the team can reap rewards.

Use rcov with your full Cucumber runs to find holes in coverage. Definitely check out Aslak Hellesoy's thoughts on the matter for more details.

9. Be DRY: Refactor and Reuse Step Definitions

Especially look for the opportunity to make reusable step definitions that are not feature specific. As a project proceeds, you should be accumulating a library of step definitions. Ideally, you will end up with step definitions that can be used across projects.

10. Use a Library (Such as Chronic) for Parsing Time in Your Step Definitions

This allows you to use time in scenarios in a natural way. This is especially useful for relative times.

  Given a user signs up for a 30 day account

Scenario: access before expiry
  When they login in 29 days
  Then they will be let in

Scenario: access after expiry
  When they login in 31 days
  Then they will be asked to renew

11. Revisit, Refactor, and Improve Your Scenarios and Steps

Look for opportunities to generalize your steps and reuse them. You want to accumulate a reusable library of steps so that writing additional features takes less and less effort over time.

12. Refactor Language and Steps to Reflect Better Understanding of Domain

This is an extension of the previous point; as your understanding of the domain and your customer's language/terminology improves, update the language used in your scenarios.

13. Use Compound Steps to Build Up Your Language

Compound steps (calling steps from steps) can help make your features more concise while still keeping your steps general—just don't get too carried away. For example:

Given /^the user (.*) exists$/ do |name|
  # ...

Given /^I log in as (.*)$/ do |name|
  # ...

Given /^(.*) is logged in$/ do |name|
  Given "the user #{name} exists"
  Given "I log in as #{name}"

14. Use Parallel Step Definitions to Support Different Implementations for Features

For example, running features against Webrat and Selenium. Put these step definitions somewhere where they won't be auto-loaded, and require them from the command line or rake task.

15. Avoid Using Conjunctive Steps

Each step should do one thing. You should not generally have step patterns containing "and." For example:

Given A and B

should be split into two steps:

Given A
And B

In Closing...

When I put out a call on Twitter, along with some of the above, I got the following:

  • Sliced, w/tomatoes, red onion, balsamic vinegar, olive oil, salt and pepper.
  • Get the kind without seeds, they stay good longer, and mix with a bit of rice vinegar to play the "flavors that mix well" game
  • slice. add humus. add bread. eat.
  • Eat them freshly picked out of an organic garden!

There are numerous ways to best utilize Cucumber and to improve your general Cucumber practices; the above list is by no means all inclusive. If you've got a great tip I missed, leave a comment—I'm always looking to learn and improve :)