relaxdiego (Mark Maglana's Technical Blog)

How We Use Cucumber

Apr 19, 2012
Est. read: 3 minutes

Lately I’ve been very involved in the conversion of our product requirements and test scripts into executable documentation via Cucumber. We initially ran into problems with deciding what goes into the feature files and what goes into the step definitions. More than once we have had to stop and ask ourselves if the feature files are too imperative or too high level. There was a lot of back and forth until we settled on the following style.

Feature File Writers Treat the System as a Black Box

A really black box with a UI that is constantly changing. In this case, the feature file writer (business analyst) pretends at one point that the system only accepts requests via mind control. At other times, she pretends that the system is controlled via a physical requisition form (signed in triplicate!). It may seem odd at first, but this way of thinking is actually very helpful because it encourages the business analyst to write business requirements rather than UI specs. Now we end up with short, readable, and very clear feature files:

Feature: Withdraw Cash

  Scenario Outline: Withdraw an amount given a balance
    Given my account has a balance of <Balance>
     When I withdraw <Requested Amount>
     Then the amount will be <Dispensed or Not>

      | Balance | Requested Amount | Dispensed or Not |
      |    $100 |              $50 | Dispensed        |
      |    $100 |             $150 | Not Dispensed    |

Notice how the above has only one When step and it doesn’t even indicate how the user withdraws the requested amount because, for all business analyst knows, the system could be driven by robotic gherbils that take the details of her request (as indicated in the When step) and manually pull levers to make things happen!

Requirements can even be shorter if the operation doesn’t require any data. For example:

Scenario Outline: A user with a given role disables notifications
  Given I have a role of <Role> in the system
   Then I <Can or Cannot Disable> notifications

    | Role         | Can or Cannot Disable |
    | System Admin | Can Disable           |
    | User         | Cannot Disable        |

Notice how I didn’t need to write a When step in the scenario outline, yet the requirements are still very clear.

Step Definitions are the Domain of the Testers

And these testers are the guys that build the robotic gherbils (otherwise known as step definitions). One of the steps above could be defined as follows:

Then /^I [Cc]an [Dd]isable notifications$/ do
  Notifier.fill_in 'username', 'jdoe'
  Notifier.fill_in 'password', '123qwe'   'login'   'disable'


In the cash withdrawal example above, one of the steps could be defined as:

When /^I withdraw $(\d+)$/ do |amount|

  # Enter PIN
  Atm.press_key '1'
  Atm.press_key '2'
  Atm.press_key '3'
  Atm.press_key 'OK'

  # Withdraw amount
  Atm.press_key 'Withdraw'
  Atm.fill_in   'Amount', amount
  Atm.press_key 'OK'

Notice how the step definitions are tied to the solution, which implies that this part only gets written after the team has decided on the UI design.

Keeping Concerns Separate

Apart from the business analyst adopting a black box thinking, we also avoid having testers initially write the feature files. This is because testers are used to poking around the app which assumes that the app is already built. Because this way of thinking is so ingrained in them, there is the risk of feature files becoming tightly coupled with one solution.

Parting Thoughts

Cucumber’s flexibility seems to be both a boon and a curse to teams, especially for those just learning about it. In our case, reading The Cucumber Book and Specification by Example pointed us to the right direction. Also, daily interaction with the helpful folks in the Cucumber mailing list further helped us find the right way to use the tool.