Setup using jest

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jest is the traditional and most popular testing solution.

TIP

You can see the described example as a code in the repository here.

Author's Note

If you are starting a new project - first consider using vite as a test-runner.
In most scenarios it is faster, easier to configure and has better documentation.

Note

This section shows the minimal configuration - for full features and nice defaults, check out the API Reference section or inspect all the options inline using editor's suggestions.

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First, install jest itself and some additional packages that you will need to get started:

npm

npm add -D jest-expect-message

yarn

yarn add -D jest-expect-message

pnpm

pnpm add -D jest-expect-message

If you are using TypeScript, install the modules required by jest to work with it:

npm

npm add -D ts-jest ts-node @types/jest

yarn

yarn add -D ts-jest ts-node @types/jest

pnpm

pnpm add -D ts-jest ts-node @types/jest

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Next, create a jest config file with the following content (at least):

jest.config.ts

import type { JestConfigWithTsJest } from 'ts-jest';

export default {
  testEnvironment: 'node',
  transform: {
    '^.+.tsx?$': ['ts-jest', {}],
  },
} as JestConfigWithTsJest;

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Next, create a file that will export functions for testing:

testing-functions.ts

// 1. Import the factory that will create functions bound to `jest`
import { createTestUtils } from '@morev/stylelint-testing-library';
// 2. Import a module that extends `jest` matchers
//    for more detailed error messages
import 'jest-expect-message';

// 3. Create testing functions
// To see all available `createTestUtils` options, please
// refer to the `API Reference` section of this documentation
// or use inline IDE suggestions.
const { createTestRule, createTestRuleConfig } = createTestUtils();

// 4. Export these functions
// Unfortunately, you will need to import these functions
// within each of your test files, as `jest` test functions
// (`describe`, `it`, `expect`, etc) only exist in the context of such files.
// If you know how to access these variables outside this context -
// feel free to create a PR or issue.
export { createTestRule, createTestRuleConfig };

testing-functions.ts (without-comments)

import { createTestUtils } from '@morev/stylelint-testing-library';
import 'jest-expect-message';

const { createTestRule, createTestRuleConfig } = createTestUtils();

export { createTestRule, createTestRuleConfig };

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Next, create a script for testing in your package.json:

package.json

{
  "name": "your-awesome-stylelint-plugin",
  "scripts": {
    "test": "node --experimental-vm-modules ./node_modules/jest/bin/jest.js"
  },
}

and you are ready to test your rules using the npm run test command:

rules/lowercase-selectors.test.ts

import { createTestRule, createTestRuleConfig } from '../testing-functions';
import { messages, ruleName } from './lowercase-selectors';

const testRule = createTestRule({ ruleName });
const testRuleConfig = createTestRuleConfig({ ruleName });

testRuleConfig({ /* ... */ });
testRule({ /* ... */ });

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We're all set!
Next, follow the instructions on the Usage page.