ESLint for Test Quality

npm install --save-dev eslint eslint-plugin-jest eslint-plugin-testing-library \
  eslint-plugin-jest-dom eslint-plugin-playwright

// eslint.config.js
import jest from 'eslint-plugin-jest';
import testingLibrary from 'eslint-plugin-testing-library';
import jestDom from 'eslint-plugin-jest-dom';
import playwright from 'eslint-plugin-playwright';

export default [
  // Unit and component tests (Jest + Testing Library)
  {
    files: ['src/**/*.test.{ts,tsx}', 'src/**/__tests__/**/*.{ts,tsx}'],
    plugins: { jest, 'testing-library': testingLibrary, 'jest-dom': jestDom },
    languageOptions: { globals: jest.environments.globals.globals },
    rules: {
      ...jest.configs['flat/recommended'].rules,
      ...testingLibrary.configs['flat/react'].rules,
      ...jestDom.configs['flat/recommended'].rules,
      'jest/no-focused-tests': 'error',
      'jest/no-disabled-tests': 'warn',
      'jest/no-conditional-expect': 'error',
      'jest/no-standalone-expect': 'error',
      'jest/valid-title': 'error',
      'jest/prefer-hooks-on-top': 'error',
      'jest/expect-expect': [
        'error',
        { assertFunctionNames: ['expect', 'expectTypeOf', 'assertOrderShape'] },
      ],
      'testing-library/prefer-user-event': 'error',
      'testing-library/no-wait-for-side-effects': 'error',
      'testing-library/no-manual-cleanup': 'error',
    },
  },
  // Playwright E2E specs
  {
    files: ['e2e/**/*.spec.ts'],
    plugins: { playwright },
    rules: {
      ...playwright.configs['flat/recommended'].rules,
      'playwright/no-focused-test': 'error',
      'playwright/no-skipped-test': 'warn',
      'playwright/no-wait-for-timeout': 'error',
      'playwright/no-conditional-in-test': 'error',
      'playwright/no-force-option': 'error',
      'playwright/expect-expect': 'error',
      'playwright/no-networkidle': 'error',
      'playwright/prefer-web-first-assertions': 'error',
    },
  },
];

// e2e/checkout.spec.ts - every line below is a lint ERROR with the config above

test.only('applies a coupon', async ({ page }) => {
  // playwright/no-focused-test: the other 84 specs in this project
  // would silently not run in CI while the build stays green.
});

test('waits for the cart to update', async ({ page }) => {
  await page.waitForTimeout(3000); // playwright/no-wait-for-timeout: flaky AND slow
  await page.click('#checkout', { force: true }); // playwright/no-force-option: bypasses actionability
});

test('shows totals', async ({ page }) => {
  const rows = await page.locator('.row').count();
  if (rows > 0) {
    expect(rows).toBeGreaterThan(0); // playwright/no-conditional-in-test
  }
  // playwright/expect-expect also fires if no assertion is reachable
});

// src/components/CouponForm.test.tsx - Jest + Testing Library violations

it('test 1', async () => {
  // jest/valid-title: meaningless title
  render(<CouponForm />);
  fireEvent.change(screen.getByRole('textbox'), { target: { value: 'SAVE10' } });
  // testing-library/prefer-user-event: fireEvent skips focus/keyboard semantics
});

it('submits the coupon', async () => {
  try {
    await submitCoupon('SAVE10');
    expect(api.apply).toHaveBeenCalled();
  } catch {
    expect(true).toBe(false); // jest/no-conditional-expect: may never run
  }
});

// tests/helpers/assert-order-shape.ts
import { expect } from 'vitest';

// Custom assertion helper used across suites
export function assertOrderShape(order: unknown): void {
  expect(order).toMatchObject({
    id: expect.stringMatching(/^ord_/),
    total: expect.any(Number),
    items: expect.arrayContaining([expect.objectContaining({ sku: expect.any(String) })]),
  });
}
// Registered above via expect-expect assertFunctionNames so tests
// that only call assertOrderShape(...) do not trip the rule.

# .github/workflows/lint.yml
name: lint
on: [pull_request]

jobs:
  eslint:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: actions/setup-node@v4
        with:
          node-version: 20
          cache: npm
      - run: npm ci
      - name: Lint (zero warnings allowed)
        run: npx eslint . --max-warnings 0

npm install --save-dev husky lint-staged
npx husky init

{
  "lint-staged": {
    "*.{ts,tsx,js}": ["eslint --fix --max-warnings 0"]
  }
}

# .husky/pre-commit
npx lint-staged