jest-generator

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Original

English

🇨🇳

Translation

Chinese

Jest Generator Skill

Jest测试生成Skill

Purpose

用途

Generate Jest-based unit tests for JavaScript and TypeScript code, following Jest conventions and best practices with proper mocking, describe blocks, and code organization.

为JavaScript和TypeScript代码生成基于Jest的单元测试，遵循Jest的规范和最佳实践，包含正确的Mock、describe代码块及代码组织结构。

When to Use

适用场景

Generate Jest tests for JavaScript/TypeScript modules
Create test files for React components
Add missing test coverage to existing code
Need Jest-specific patterns (mocks, spies, snapshots)

为JavaScript/TypeScript模块生成Jest测试
为React组件创建测试文件
为现有代码补充缺失的测试覆盖率
需要使用Jest特定模式（Mock、Spy、快照）

Test File Naming

测试文件命名规范

Source to Test Mapping:

src/components/Feature.tsx

→

src/components/Feature.test.tsx

src/utils/validator.ts

→

src/utils/validator.test.ts

src/models/User.ts

→

src/models/User.test.ts

源码与测试文件映射：

src/components/Feature.tsx

→

src/components/Feature.test.tsx

src/utils/validator.ts

→

src/utils/validator.test.ts

src/models/User.ts

→

src/models/User.test.ts

Running Tests

运行测试

bash

undefined

bash

undefined

Preferred: Using bun (faster)

推荐：使用bun（速度更快）

bun test

Run specific file

运行指定文件

bun test src/utils/validator.test.ts

Run with coverage

带覆盖率统计运行

bun test --coverage

Watch mode

监听模式

bun test --watch

Alternative: Using npm

替代方案：使用npm

npm test npm test -- --coverage

undefined

npm test npm test -- --coverage

undefined

Jest Test Structure

Jest测试结构

typescript

import { functionToTest, ClassToTest } from './Feature'

jest.mock('./dependency')

describe('ModuleName', () => {
  beforeEach(() => {
    jest.clearAllMocks()
  })

  afterEach(() => {
    jest.restoreAllMocks()
  })

  describe('ClassName', () => {
    let instance: ClassToTest

    beforeEach(() => {
      instance = new ClassToTest()
    })

    it('should return expected result with valid input', () => {
      // Arrange
      const input = { key: 'value' }
      const expected = { processed: true }

      // Act
      const result = instance.method(input)

      // Assert
      expect(result).toEqual(expected)
    })

    it('should throw error with invalid input', () => {
      expect(() => instance.method(null)).toThrow('Invalid input')
    })
  })
})

typescript

import { functionToTest, ClassToTest } from './Feature'

jest.mock('./dependency')

describe('ModuleName', () => {
  beforeEach(() => {
    jest.clearAllMocks()
  })

  afterEach(() => {
    jest.restoreAllMocks()
  })

  describe('ClassName', () => {
    let instance: ClassToTest

    beforeEach(() => {
      instance = new ClassToTest()
    })

    it('should return expected result with valid input', () => {
      // Arrange
      const input = { key: 'value' }
      const expected = { processed: true }

      // Act
      const result = instance.method(input)

      // Assert
      expect(result).toEqual(expected)
    })

    it('should throw error with invalid input', () => {
      expect(() => instance.method(null)).toThrow('Invalid input')
    })
  })
})

Jest-Specific Patterns

Jest特定模式

Mocking

Mocking（模拟）

typescript

// Mock entire module
jest.mock('./api', () => ({
  fetchData: jest.fn(),
}))

// Mock with implementation
const mockFn = jest.fn((x: number) => x * 2)

// Spy on method
const spy = jest.spyOn(obj, 'method').mockReturnValue('mocked')
spy.mockRestore()

typescript

// 模拟整个模块
jest.mock('./api', () => ({
  fetchData: jest.fn(),
}))

// 带实现逻辑的模拟
const mockFn = jest.fn((x: number) => x * 2)

// 监视方法
const spy = jest.spyOn(obj, 'method').mockReturnValue('mocked')
spy.mockRestore()

Async Testing

异步测试

typescript

it('should resolve with data', async () => {
  const result = await asyncFunction()
  expect(result).toBeDefined()
})

it('should reject with error', async () => {
  await expect(asyncFunction()).rejects.toThrow('Error')
})

typescript

it('should resolve with data', async () => {
  const result = await asyncFunction()
  expect(result).toBeDefined()
})

it('should reject with error', async () => {
  await expect(asyncFunction()).rejects.toThrow('Error')
})

Timers

定时器测试

typescript

beforeEach(() => jest.useFakeTimers())
afterEach(() => jest.useRealTimers())

it('should execute after timeout', () => {
  const callback = jest.fn()
  setTimeout(callback, 1000)
  jest.advanceTimersByTime(1000)
  expect(callback).toHaveBeenCalled()
})

typescript

beforeEach(() => jest.useFakeTimers())
afterEach(() => jest.useRealTimers())

it('should execute after timeout', () => {
  const callback = jest.fn()
  setTimeout(callback, 1000)
  jest.advanceTimersByTime(1000)
  expect(callback).toHaveBeenCalled()
})

Common Matchers

常用匹配器

typescript

// Equality
expect(value).toBe(expected)
expect(value).toEqual(expected)

// Truthiness
expect(value).toBeTruthy()
expect(value).toBeNull()
expect(value).toBeDefined()

// Arrays/Objects
expect(array).toContain(item)
expect(obj).toHaveProperty('key')

// Functions/Promises
expect(fn).toThrow('error')
await expect(promise).resolves.toBe(value)

// Mock functions
expect(mockFn).toHaveBeenCalled()
expect(mockFn).toHaveBeenCalledWith(arg)

typescript

// 相等性
expect(value).toBe(expected)
expect(value).toEqual(expected)

// 真值判断
expect(value).toBeTruthy()
expect(value).toBeNull()
expect(value).toBeDefined()

// 数组/对象
expect(array).toContain(item)
expect(obj).toHaveProperty('key')

// 函数/Promise
expect(fn).toThrow('error')
await expect(promise).resolves.toBe(value)

// 模拟函数
expect(mockFn).toHaveBeenCalled()
expect(mockFn).toHaveBeenCalledWith(arg)

React Component Testing

React组件测试

typescript

import { render, screen, fireEvent } from '@testing-library/react'
import '@testing-library/jest-dom'
import { Button } from './Button'

describe('Button', () => {
  it('should call onClick when clicked', () => {
    const handleClick = jest.fn()
    render(<Button onClick={handleClick}>Click me</Button>)
    fireEvent.click(screen.getByText('Click me'))
    expect(handleClick).toHaveBeenCalledTimes(1)
  })
})

typescript

import { render, screen, fireEvent } from '@testing-library/react'
import '@testing-library/jest-dom'
import { Button } from './Button'

describe('Button', () => {
  it('should call onClick when clicked', () => {
    const handleClick = jest.fn()
    render(<Button onClick={handleClick}>Click me</Button>)
    fireEvent.click(screen.getByText('Click me'))
    expect(handleClick).toHaveBeenCalledTimes(1)
  })
})

Quality Checklist

质量检查清单

Test file properly named (
```
<module>.test.ts
```
)
All exported functions/classes tested
Happy path and edge cases included
Error conditions tested
External dependencies mocked
Tests organized with describe blocks
beforeEach/afterEach for setup/cleanup
Descriptive test names
Coverage ≥ 80%

测试文件命名规范（
```
<module>.test.ts
```
）
所有导出的函数/类均已测试
包含正常流程和边缘场景测试
测试了错误情况
外部依赖已被Mock
测试用describe块组织
使用beforeEach/afterEach进行初始化/清理
测试名称具有描述性
覆盖率≥80%

Best Practices

最佳实践

Use descriptive test names:
```
should <expected> when <condition>
```
Organize with describe blocks
Mock external dependencies only
Test user behavior for components
Use test.each for parametrized tests
Keep tests independent
Test error conditions
Aim for 80%+ coverage

使用具有描述性的测试名称：
```
should <预期结果> when <条件>
```
用describe块组织测试
仅Mock外部依赖
针对组件测试用户行为
使用test.each进行参数化测试
保持测试独立性
测试错误条件
目标覆盖率≥80%