Cucumber & Gherkin Skill

BDD testing framework with plain-text executable specifications. Gherkin syntax with step definitions in Ruby, JavaScript, Java, or Python.

Core Concepts

Cucumber reads executable specifications in plain text and validates software behavior. Gherkin is the structured grammar making plain text machine-readable.

┌────────────┐                 ┌──────────────┐                 ┌───────────┐
│   Steps    │                 │     Step     │                 │           │
│ in Gherkin ├──matched with──>│ Definitions  ├───manipulates──>│  System   │
└────────────┘                 └──────────────┘                 └───────────┘

Gherkin Syntax Quick Reference

Primary Keywords

Feature: Short description
  Optional multi-line description explaining the feature.
  
  Background:
    Given common setup steps for all scenarios
  
  Rule: Business rule grouping (Gherkin 6+)
    
    Scenario: Concrete example illustrating the rule
      Given an initial context (past tense, setup)
      When an action occurs (present tense, trigger)
      Then expected outcome (assertion)
      And additional step
      But negative assertion
    
    Scenario Outline: Parameterized scenario
      Given there are <start> items
      When I remove <remove> items
      Then I should have <remaining> items
      
      Examples:
        | start | remove | remaining |
        |    12 |      5 |         7 |
        |    20 |      5 |        15 |

Step Keywords

Keyword	Purpose	Example
`Given`	Setup/precondition	`Given I am logged in as "admin"`
`When`	Action/trigger	`When I click the submit button`
`Then`	Assertion/outcome	`Then I should see "Success"`
`And`	Continue previous type	`And I have 3 items in my cart`
`But`	Negative continuation	`But I should not see "Error"`
`*`	Bullet-style step	`* I have eggs`

Data Structures

Data Tables - tabular data:

Given the following users exist:
  | name   | email              | role  |
  | Alice  | alice@example.com  | admin |
  | Bob    | bob@example.com    | user  |

Doc Strings - multi-line text:

Given a blog post with content:
  """markdown
  # My Post Title
  
  This is the content of my blog post.
  """

Step Definitions

Match Gherkin steps to code. Use Cucumber Expressions (preferred) or Regular Expressions.

Ruby

Given('I have {int} cucumbers in my belly') do |count|
  @belly = Belly.new
  @belly.eat(count)
end

When('I wait {int} hour(s)') do |hours|
  @belly.wait(hours)
end

Then('my belly should growl') do
  expect(@belly.growling?).to be true
end

# With data table
Given('the following users exist:') do |table|
  table.hashes.each do |row|
    User.create!(row)
  end
end

JavaScript

const { Given, When, Then } = require('@cucumber/cucumber');

Given('I have {int} cucumbers in my belly', function(count) {
  this.belly = new Belly();
  this.belly.eat(count);
});

When('I wait {int} hour(s)', async function(hours) {
  await this.belly.wait(hours);
});

Then('my belly should growl', function() {
  expect(this.belly.isGrowling()).toBe(true);
});

// With data table
Given('the following users exist:', async function(dataTable) {
  for (const row of dataTable.hashes()) {
    await User.create(row);
  }
});

Java

public class StepDefinitions {
    @Given("I have {int} cucumbers in my belly")
    public void iHaveCucumbersInMyBelly(int count) {
        belly = new Belly();
        belly.eat(count);
    }
    
    @When("I wait {int} hour(s)")
    public void iWaitHours(int hours) {
        belly.wait(hours);
    }
    
    @Then("my belly should growl")
    public void myBellyShouldGrowl() {
        assertTrue(belly.isGrowling());
    }
}

Cucumber Expressions

Built-in parameter types: {int}, {float}, {word}, {string}, {} (anonymous)

Optional text: cucumber(s) matches "cucumber" or "cucumbers" Alternative text: color/colour matches "color" or "colour"

Hooks

Scenario Hooks

# Ruby
Before do |scenario|
  # runs before each scenario
end

After do |scenario|
  # runs after each scenario
  screenshot if scenario.failed?
end

// JavaScript
const { Before, After } = require('@cucumber/cucumber');

Before(async function(scenario) {
  // runs before each scenario
});

After(async function(scenario) {
  // runs after each scenario
  if (scenario.result.status === 'FAILED') {
    await this.screenshot();
  }
});

Conditional Hooks (with tags)

Before('@database') do
  DatabaseCleaner.start
end

After('@database') do
  DatabaseCleaner.clean
end

Before({ tags: '@browser and not @headless' }, async function() {
  this.browser = await launchBrowser();
});

Global Hooks

BeforeAll do
  # once before any scenario
end

AfterAll do
  # once after all scenarios
end

Best Practices

Declarative over Imperative

Good (declarative):

When "Bob" logs in
Then he sees his dashboard

Avoid (imperative):

When I visit "/login"
And I enter "bob" in "username"
And I enter "secret" in "password"
And I click "Login"
Then I should see "Dashboard"

Focus on Behavior, Not Implementation

Describe what the system does, not how
Use domain language stakeholders understand
Keep scenarios short (3-5 steps recommended)
One behavior per scenario

Background Usage

Keep backgrounds short (≤4 lines)
Use only for essential shared context
Move implementation details to step definitions

Running Cucumber

# Ruby
bundle exec cucumber
cucumber --tags "@smoke and not @wip"
cucumber features/login.feature:10  # specific line

# JavaScript
npx cucumber-js
npx cucumber-js --tags "@smoke"

# Java (with Maven)
mvn test -Dcucumber.filter.tags="@smoke"

Additional References

For comprehensive details, see reference files:

references/gherkin-syntax.md - Complete Gherkin language reference
references/step-definitions.md - Step definition patterns by language
references/hooks-config.md - Hooks, configuration, and runners
references/best-practices.md - Anti-patterns and advanced patterns

cucumber-gherkin