AgentSkillsCN

typescript-test

提供基于 Jest 的 TypeScript 测试专业知识与最佳实践。确保测试结构合理、Mock 策略得当、异步处理模式规范，并持续优化测试覆盖率。擅长单元测试、集成测试、以 describe/it 块组织测试、Jest.mock 模式、快照测试，以及为 UI 组件集成测试库。 适用场景：编写 TypeScript 测试文件（.spec.ts、.test.ts）、以 describe/it/test 块组织测试、使用 jest.mock/jest.spyOn 实现 Mock 模拟、以 async/await 或 Promise 测试异步代码、创建测试用例与辅助函数、实施快照测试、使用 Testing Library 测试 React 组件、衡量并提升代码覆盖率，或为 TypeScript 项目配置 Jest 测试环境。

SKILL.md
--- frontmatter
name: typescript-test
description: |
  Provides Jest-based TypeScript testing expertise and best practices. Ensures proper test structure, mocking strategies, async handling patterns, and coverage optimization. Specializes in unit testing, integration testing, test organization with describe/it blocks, jest.mock patterns, snapshot testing, and testing library integration for UI components.
  Use when: writing TypeScript test files (.spec.ts, .test.ts), structuring tests with describe/it/test blocks, implementing mocks with jest.mock/jest.spyOn, testing async code with async/await or promises, creating test fixtures and helpers, implementing snapshot tests, testing React components with Testing Library, measuring and improving code coverage, or configuring Jest for TypeScript projects.

TypeScript Testing Code Guide

Test File Structure

One-to-one matching with the file under test. Test files should be located in the same directory as the target file.

File Naming

Format: {target-file-name}.spec.ts.

Example: user.service.ts → user.service.spec.ts

Test Framework

Use Jest. Maintain consistency within the project.

Test Hierarchy

Organize by method (function) unit as major sections, and by test case as minor sections. Complex methods can have intermediate sections by scenario.

Test Coverage Selection

Omit obvious or overly simple logic (simple getters, constant returns). Prioritize testing business logic, conditional branches, and code with external dependencies.

Test Case Composition

At least one basic success case is required. Focus primarily on failure cases, boundary values, edge cases, and exception scenarios.

Test Independence

Each test should be executable independently. No test execution order dependencies. Initialize shared state for each test.

Given-When-Then Pattern

Structure test code in three stages—Given (setup), When (execution), Then (assertion). Separate stages with comments or blank lines for complex tests.

Test Data

Use hardcoded meaningful values. Avoid random data as it causes unreproducible failures. Fix seeds if necessary.

Mocking Principles

Mock external dependencies (API, DB, file system). For modules within the same project, prefer actual usage; mock only when complexity is high.

Test Reusability

Extract repeated mocking setups, fixtures, and helper functions into common utilities. Be careful not to harm test readability through excessive abstraction.

Integration/E2E Testing

Unit tests are the priority. Write integration/E2E tests when complex flows or multi-module interactions are difficult to understand from code alone. Place in separate directories (tests/integration, tests/e2e).

Test Naming

Test names should clearly express "what is being tested". Recommended format: "should do X when Y". Focus on behavior rather than implementation details.

Assertion Count

Multiple related assertions in one test are acceptable, but separate tests when validating different concepts.

Structure

Group methods/functionality with describe, write individual cases with it. Can classify scenarios with nested describe.

Mocking

Utilize Jest's jest.mock(), jest.spyOn(). Mock external modules at the top level; change behavior per test with mockReturnValue, mockImplementation.

Async Testing

Use async/await. Test Promise rejection with await expect(fn()).rejects.toThrow() form.

Setup/Teardown

Use beforeEach, afterEach for common setup/cleanup. Use beforeAll, afterAll only for heavy initialization (DB connection, etc.).

Type Safety

Type check test code too. Minimize as any or @ts-ignore. Use type guards or type assertions explicitly when needed.

Test Utils Location

For single-file use, place at bottom of same file. For multi-file sharing, use __tests__/utils or test-utils directory.

Coverage

Code coverage is a reference metric. Focus on meaningful test coverage rather than blindly pursuing 100%.