Comparison / Mapping of Gherkin to Jest

Gherkin is a well defined language, which is easy to parse and read by both humans and machines, not only accessible to non-technical stack-holders, but also easier for experienced developers to understand the intended behaviour of the system, and organize test cases effectively. It naturally matches the structure of Jest test files, aligning the behavior-driven development (BDD) approach to a more structured and organized testing methodology.

Gherkin keywords	Jest methods
Feature	describe()
Scenario	test() / it()
Examples	test.each()
Background	beforeAll()
Steps	Code statements with //@STEP comments

Example: Mapping a Gherkin Scenario to Jest

Here’s how a Gherkin scenario translates perfectly into a Jest test:

• Gherkin:

./docs/features/rounding.feature

Feature: Rounding methods of Math

Scenario Outline: Integer pattern
  Given input number is <num>
  When rounding with <method>
  Then rounded number is <result>

Examples:
| num    | method | result |
| 1234.1 | "ceil" | 1235   |
| 1234.9 | "ceil" | 1235   |
| -1234.1| "ceil" | -1234  |
| -1234.9| "ceil" | -1234  |
| 1234.1 | "floor"| 1234   |
| 1234.9 | "floor"| 1234   |
| -1234.1| "floor"| -1235  |
| -1234.9| "floor"| -1235  |
| 1234.5 | "round"| 1235   |
| 1234.4 | "round"| 1234   |
| -1234.5| "round"| -1234  |
| -1234.6| "round"| -1235  |

• Jest:

./tests/rounding.test.ts

import { describe, test, expect } from '@jest/globals';

describe('Rounding methods of Math', () => {
  test.each([
    { num: 1234.1, method: 'ceil', result: 1235 },
    { num: 1234.9, method: 'ceil', result: 1235 },
    { num: -1234.1, method: 'ceil', result: -1234 },
    { num: -1234.9, method: 'ceil', result: -1234 },
    { num: 1234.1, method: 'floor', result: 1234 },
    { num: 1234.9, method: 'floor', result: 1234 },
    { num: -1234.1, method: 'floor', result: -1235 },
    { num: -1234.9, method: 'floor', result: -1235 },
    { num: 1234.5, method: 'round', result: 1235 },
    { num: 1234.4, method: 'round', result: 1234 },
    { num: -1234.5, method: 'round', result: -1234 },
    { num: -1234.6, method: 'round', result: -1235 }
  ])('Integer pattern for $method', ({ num, method, result }) => {
    //@Given input number is <num>
    expect(typeof num).toBe('number');

    //@When rounding with <method>
    expect(Math).toHaveProperty(method);

    //@Then rounded number is <result>
    expect(Math[method](num)).toEqual(result);
  });
});

In this example, the Gherkin feature and scenario outline are mapped directly into Jest's describe(), test.each(), and expect() functions, with comments marking the corresponding Gherkin steps (//@STEP). This provides a clear 1:1 mapping, demonstrating how the two frameworks align in structure and logic.