JavaScript 与 TypeScript Jest 测试指引

作者原文

Best practices for writing JavaScript/TypeScript tests using Jest, including mocking strategies, test structure, and common patterns.

SkillPi 解读

能完成的任务

提供测试命名、依赖模拟、异步断言、快照及 React 组件测试指引。

适合谁

使用 Jest 编写或审阅测试的 JavaScript、TypeScript 开发者。

输入和输出

输入被测代码与期望的可观察行为；输出测试结构及断言/模拟指引。

软件、账号及付费要求

需要使用 Jest 的 JavaScript/TypeScript 项目；React 部分提及 React Testing Library，未指定付费服务。 使用时由宿主核对并授权实际文件读写和外部服务。文档引用域名（非运行白名单）：未列出 HTTP(S) 域名。

限制与区别

这是简要模式指引，不是测试覆盖率或正确性的证明。快照变更与模拟仍需审阅。

实测状态

未测试

安全评级与访问范围

caution · 静态证据核验，不代表运行安全保证。

需要使用 Jest 的 JavaScript/TypeScript 项目；React 部分提及 React Testing Library，未指定付费服务。 使用时由宿主核对并授权实际文件读写和外部服务。文档引用域名（非运行白名单）：未列出 HTTP(S) 域名。

使用前请由宿主核对并授权实际文件读写、外部服务和联网目的地；本站的核验不会授予任何运行权限。

原始 SKILL.md

---
name: javascript-typescript-jest
description: 'Best practices for writing JavaScript/TypeScript tests using Jest, including mocking strategies, test structure, and common patterns.'
---

### Test Structure
- Name test files with `.test.ts` or `.test.js` suffix
- Place test files next to the code they test or in a dedicated `__tests__` directory
- Use descriptive test names that explain the expected behavior
- Use nested describe blocks to organize related tests
- Follow the pattern: `describe('Component/Function/Class', () => { it('should do something', () => {}) })`

### Effective Mocking
- Mock external dependencies (APIs, databases, etc.) to isolate your tests
- Use `jest.mock()` for module-level mocks
- Use `jest.spyOn()` for specific function mocks
- Use `mockImplementation()` or `mockReturnValue()` to define mock behavior
- Reset mocks between tests with `jest.resetAllMocks()` in `afterEach`

### Testing Async Code
- Always return promises or use async/await syntax in tests
- Use `resolves`/`rejects` matchers for promises
- Set appropriate timeouts for slow tests with `jest.setTimeout()`

### Snapshot Testing
- Use snapshot tests for UI components or complex objects that change infrequently
- Keep snapshots small and focused
- Review snapshot changes carefully before committing

### Testing React Components
- Use React Testing Library over Enzyme for testing components
- Test user behavior and component accessibility
- Query elements by accessibility roles, labels, or text content
- Use `userEvent` over `fireEvent` for more realistic user interactions

## Common Jest Matchers
- Basic: `expect(value).toBe(expected)`, `expect(value).toEqual(expected)`
- Truthiness: `expect(value).toBeTruthy()`, `expect(value).toBeFalsy()`
- Numbers: `expect(value).toBeGreaterThan(3)`, `expect(value).toBeLessThanOrEqual(3)`
- Strings: `expect(value).toMatch(/pattern/)`, `expect(value).toContain('substring')`
- Arrays: `expect(array).toContain(item)`, `expect(array).toHaveLength(3)`
- Objects: `expect(object).toHaveProperty('key', value)`
- Exceptions: `expect(fn).toThrow()`, `expect(fn).toThrow(Error)`
- Mock functions: `expect(mockFn).toHaveBeenCalled()`, `expect(mockFn).toHaveBeenCalledWith(arg1, arg2)`

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