AgentSkillsCN

advanced-js-mocking-patterns

为Jest与Vitest提供高级模拟模式，涵盖模块模拟、Spy对象以及虚假定时器。主动启用以下场景：(1) 模块模拟；(2) 通过Spy进行部分模拟；(3) 管理模拟生命周期；(4) 为依赖时间的代码设置虚假定时器；(5) 实现复杂的模拟场景。触发指令包括：“jest.mock”“vi.mock”“spyOn”“fakeTimers”“mockImplementation”“mockReturnValue”“模拟生命周期”。

SKILL.md
--- frontmatter
name: advanced-js-mocking-patterns
version: "1.0"
description: >
  Advanced mocking patterns for Jest and Vitest including module mocking, spies, and fake timers.
  PROACTIVELY activate for: (1) Module mocking, (2) Partial mocking with spies,
  (3) Mock lifecycle management, (4) Fake timers for time-dependent code, (5) Complex mock implementations.
  Triggers: "jest.mock", "vi.mock", "spyOn", "fakeTimers", "mockImplementation", "mockReturnValue", "mock lifecycle"
core-integration:
  techniques:
    primary: ["exhaustive_edge_case_enumeration"]
    secondary: ["completeness_verification"]
  contracts:
    input: "none"
    output: "none"
  patterns: "none"
  rubrics: "none"

Advanced JS Mocking Patterns Skill

Metadata (Tier 1)

Keywords: jest.mock, vi.mock, spyOn, fakeTimers, mockImplementation

File Patterns: *.test.ts, *.spec.js

Modes: testing_frontend, testing_backend

Instructions (Tier 2)

Module Mocking

typescript
// Mock entire module
jest.mock('axios');

import axios from 'axios';

test('fetches data', async () => {
  (axios.get as jest.Mock).mockResolvedValue({ data: { id: 1 } });

  const result = await fetchUser(1);

  expect(result).toEqual({ id: 1 });
});

Spies (Partial Mocking)

typescript
const obj = {
  method1: () => 'original',
  method2: () => 'original'
};

const spy = jest.spyOn(obj, 'method1');
spy.mockReturnValue('mocked');

obj.method1(); // 'mocked'
obj.method2(); // 'original' (not mocked)

expect(spy).toHaveBeenCalled();

Mock Lifecycle

typescript
beforeEach(() => {
  jest.clearAllMocks();  // Reset call counts
});

afterEach(() => {
  jest.restoreAllMocks();  // Restore original implementations
});

Fake Timers

typescript
jest.useFakeTimers();

test('debounce function', () => {
  const callback = jest.fn();
  const debounced = debounce(callback, 1000);

  debounced();
  debounced();
  debounced();

  jest.advanceTimersByTime(1000);

  expect(callback).toHaveBeenCalledTimes(1);  // Only last call
});

Mock Implementations

typescript
const mock = jest.fn()
  .mockImplementationOnce(() => 'first')
  .mockImplementationOnce(() => 'second')
  .mockImplementation(() => 'default');

mock(); // 'first'
mock(); // 'second'
mock(); // 'default'

Anti-Patterns

  • •Not clearing mocks between tests
  • •Over-mocking (testing implementation)
  • •Mocking internal modules
  • •Forgetting to restore timers