Jest Cucumber

Execute Gherkin scenarios in Jest

Overview

jest-cucumber is an alternative to Cucumber.js that runs on top on Jest. Instead of using describe and it blocks, you instead write a Jest test for each scenario, and then define Given, When, and Then step definitions inside of your Jest tests. jest-cucumber then allows you to link these Jest tests to your feature files and ensure that they always stay in sync.

Motivation

Jest is an excellent test runner with great features like parallel test execution, mocking, snapshots, code coverage, etc. If you're using VS Code, there's also a terrific Jest extension that allows you get realtime feedback as you're writing your tests and easily debug failing tests individually. Cucumber is a popular tool for doing Acceptance Test-Driven Development and creating business-readable executable specifications. This library aims to achieve the best of both worlds, and even run your unit tests and acceptance tests in the same test runner.

Getting Started

Install Jest Cucumber:

npm install jest-cucumber --save-dev

Add a Feature file:

Feature: Rocket Launching

Scenario: Launching a SpaceX rocket
  Given I am Elon Musk attempting to launch a rocket into space
  When I launch the rocket
  Then the rocket should end up in space
  And the booster(s) should land back on the launch pad
  And nobody should doubt me ever again

Add the following to your Jest configuration:

  "testMatch": [
    "**/*.steps.js"
  ],

Add a step definition file that links to your feature file:

//rocket-launching.steps.js

import { defineFeature, loadFeature } from 'jest-cucumber';

const feature = loadFeature('./features/RocketLaunching.feature');

Add a Jest test for each scenario into your step definition file:

//rocket-launching.steps.js

import { defineFeature, loadFeature } from 'jest-cucumber';

const feature = loadFeature('./features/RocketLaunching.feature');

defineFeature(feature, test => {
  test('Launching a SpaceX rocket', ({ given, when, then }) => {

  });
});

Add step definitions to your scenario Jest tests:

//rocket-launching.steps.js

import { defineFeature, loadFeature } from 'jest-cucumber';
import Rocket from '../Rocket';

const feature = loadFeature('./features/RocketLaunching.feature');

defineFeature(feature, test => {
  test('Launching a SpaceX rocket', ({ given, when, then }) => {
    let rocket;

    given('I am Elon Musk attempting to launch a rocket into space', () => {
      rocket = new Rocket();
    });

    when('I launch the rocket', () => {
      rocket.launch();
    });

    then('the rocket should end up in space', () => {
      expect(rocket.isInSpace).toBe(true);
    });

    then('the booster(s) should land back on the launch pad', () => {
      expect(rocket.boostersLanded).toBe(true);
    });

    then('nobody should doubt me ever again', () => {
      expect('people').not.toBe('haters');
    });
  });
});

Additional Documentation

• Gherkin tables
• Step definition arguments
• Scenario outlines
• Re-using step definitions
• Configuration options
• Running the examples
• Using Docstrings