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testland/jest-tests

Configures and runs Jest - Meta-built batteries-included JS/TS unit framework with built-in `expect`, snapshot testing, mocking (`jest.mock`, `jest.fn`, `jest.spyOn`, manual `__mocks__/`), test environment selection (`jsdom` / `node`), parallel workers, coverage via Istanbul, watch mode, and CI integration via `--ci` flag. Use when the user works with React (CRA / older Next.js) or Node services and needs the most ecosystem-supported JS test framework.

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Files

coverage-ci-eslint.mdreferences/

Jest coverage, CI, and ESLint

Deep reference for jest-tests SKILL.md. Consult when wiring coverage gating, CI runs (--ci), JUnit reporting, or the ESLint test-globals config.

Coverage

jest --coverage

Output formats: text, lcov, html, json, json-summary. Configure via coverageReporters in jest.config.js. The coverageThreshold field fails the run if coverage drops below thresholds.

For the coverageThreshold per-file pattern:

coverageThreshold: {
  './src/critical-module/': {
    branches: 95,
    statements: 95,
  },
  './src/legacy/': {
    branches: 50,
  },
},

CI integration

Per Jest CLI, --ci flag is critical for CI runs:

# .github/workflows/test.yml
- run: npm ci
- run: npx jest --ci --coverage --maxWorkers=2 --reporters=default --reporters=jest-junit
- uses: codecov/codecov-action@v4
  with: { files: ./coverage/lcov.info }

--ci semantics:

  • Disables snapshot writing on missing snapshots (fails instead - prevents accidental snapshot generation in CI)
  • Disables interactive prompts
  • Equivalent to process.env.CI=true

--maxWorkers=2 is typical for GitHub-hosted runners (2 CPUs); tune per runner specs.

For JUnit XML output (consumable by junit-xml-analysis in qa-test-reporting):

npm install --save-dev jest-junit
JEST_JUNIT_OUTPUT_FILE=./test-results/junit.xml \
  jest --ci --reporters=default --reporters=jest-junit

ESLint integration

Per jest-start:

// eslint.config.js
import {defineConfig} from 'eslint/config';
import globals from 'globals';

export default defineConfig([
  {
    files: ['**/*.test.js', '**/*.spec.js'],
    languageOptions: {
      globals: { ...globals.jest },
    },
  },
]);

Or via eslint-plugin-jest:

npm install --save-dev eslint-plugin-jest
{
  "overrides": [{
    "files": ["**/*.test.js", "**/*.spec.js"],
    "plugins": ["jest"],
    "extends": ["plugin:jest/recommended"]
  }]
}

references

configuration.md

coverage-ci-eslint.md

mocking.md

SKILL.md

tile.json