jest

When to use this skill

• Write unit tests and integration tests with Jest
• Set up Jest in a project
• Use Jest matchers and assertions
• Test asynchronous code
• Mock functions, modules, and dependencies
• Create snapshot tests
• Configure Jest for different environments
• Use Jest with TypeScript, React, Vue, or other frameworks
• Run tests and generate coverage reports
• Use Jest CLI commands
• Set up test environments (jsdom, node)
• Use Jest with Vite (via vite-jest, though Vitest is recommended for new Vite projects)

How to use this skill

1. Identify the topic from the user's request:
   • Getting started/快速开始 →

     examples/getting-started/installation.md

     or

     examples/getting-started/using-matchers.md

   • Testing/测试 →

     examples/testing/asynchronous.md

     or

     examples/testing/setup-teardown.md

   • Mock functions/Mock 函数 →

     examples/testing/mock-functions.md

   • Mock modules/Mock 模块 →

     examples/testing/manual-mocks.md

   • Snapshots/快照 →

     examples/testing/snapshot-testing.md

   • Configuration/配置 →

     examples/configuration/jest-config.md

   • CLI/命令行 →

     examples/configuration/cli-options.md

2. Load the appropriate example file from the

   examples/

   directory:
   Getting Started (快速开始) -

   examples/getting-started/

   :

   • examples/getting-started/installation.md

     - Installing Jest and basic setup

   • examples/getting-started/using-matchers.md

     - Using Jest matchers and assertions
   Testing (测试) -

   examples/testing/

   :

   • examples/testing/asynchronous.md

     - Testing asynchronous code

   • examples/testing/setup-teardown.md

     - Setup and teardown functions

   • examples/testing/mock-functions.md

     - Mocking functions

   • examples/testing/manual-mocks.md

     - Manual mocks

   • examples/testing/snapshot-testing.md

     - Snapshot testing

   • examples/testing/timer-mocks.md

     - Mocking timers

   • examples/testing/es6-class-mocks.md

     - Mocking ES6 classes
   Configuration (配置) -

   examples/configuration/

   :

   • examples/configuration/jest-config.md

     - Jest configuration options

   • examples/configuration/cli-options.md

     - CLI options and flags

   • examples/configuration/babel.md

     - Using Jest with Babel

   • examples/configuration/typescript.md

     - Using Jest with TypeScript
   Guides (指南) -

   examples/guides/

   :

   • examples/guides/migrating-to-jest.md

     - Migrating to Jest

   • examples/guides/testing-react-apps.md

     - Testing React applications

   • examples/guides/testing-vue-apps.md

     - Testing Vue applications
3. Follow the specific instructions in that example file for syntax, structure, and best practices
   Important Notes:
   • All examples follow Jest best practices
   • Examples include both JavaScript and TypeScript versions where applicable
   • Each example file includes key concepts, code examples, and key points
   • Always check the example file for best practices and common patterns
4. Reference API documentation in the

   api/

   directory when needed:

   • api/expect.md

     - expect() API and matchers

   • api/mock-functions.md

     - Mock functions API

   • api/jest-object.md

     - Jest object API

   • api/test.md

     - test() and describe() API

   • api/cli.md

     - CLI commands and options
5. Use templates from the

   templates/

   directory:

   • templates/jest-config.md

     - Jest configuration templates

   • templates/test-template.md

     - Test file templates

   • templates/setup-file.md

     - Setup file templates

Doc mapping (one-to-one with https://jestjs.io/docs/getting-started, https://jestjs.io/docs/api)

• examples/getting-started/installation.md

  → https://jestjs.io/docs/getting-started

• examples/getting-started/using-matchers.md

  → https://jestjs.io/docs/using-matchers

• examples/testing/asynchronous.md

  → https://jestjs.io/docs/asynchronous

• examples/testing/setup-teardown.md

  → https://jestjs.io/docs/setup-teardown

• examples/testing/mock-functions.md

  → https://jestjs.io/docs/mock-functions

• examples/testing/manual-mocks.md

  → https://jestjs.io/docs/manual-mocks

• examples/testing/snapshot-testing.md

  → https://jestjs.io/docs/snapshot-testing

• examples/testing/timer-mocks.md

  → https://jestjs.io/docs/timer-mocks

• examples/testing/es6-class-mocks.md

  → https://jestjs.io/docs/es6-class-mocks

• examples/configuration/jest-config.md

  → https://jestjs.io/docs/configuration

• examples/configuration/cli-options.md

  → https://jestjs.io/docs/cli

• api/expect.md

  → https://jestjs.io/docs/expect

• api/mock-functions.md

  → https://jestjs.io/docs/mock-functions

• api/jest-object.md

  → https://jestjs.io/docs/jest-object

• api/test.md

  → https://jestjs.io/docs/api#testname-fn-timeout

• api/cli.md

  → https://jestjs.io/docs/cli

Examples and Templates

examples/

• Identify the topic from the user's request
• Load the appropriate example file from the mapping above
• Follow the instructions, syntax, and best practices in that file
• Adapt the code examples to your specific use case

• Reference templates in

  templates/

  directory for common scaffolding
• Adapt templates to your specific needs and coding style

Best Practices

1. Write descriptive test names: Use clear, descriptive test names
2. Use appropriate matchers: Choose the right matcher for each assertion
3. Mock external dependencies: Mock external APIs, databases, and services
4. Test edge cases: Test both happy paths and error cases
5. Keep tests isolated: Each test should be independent
6. Use setup and teardown: Clean up resources properly
7. Snapshot testing: Use snapshots for UI components, but review changes
8. Coverage goals: Aim for meaningful coverage, not just high percentages
9. Organize tests: Group related tests using describe blocks
10. Async testing: Properly handle async code with async/await or promises

Resources

• Official Documentation: https://jestjs.io/
• Getting Started: https://jestjs.io/docs/getting-started
• API Reference: https://jestjs.io/docs/api
• GitHub Repository: https://github.com/jestjs/jest

Keywords