skills/ LambdaTest/agent-skills

vitest-skill

Generates Vitest tests in JavaScript/TypeScript with Vite-native speed. Jest-compatible API with ESM support and HMR. Use when user mentions "Vitest", "vi.mock", "vitest.config". Triggers on: "Vitest", "vi.mock", "vi.fn", "Vite test", "vitest config".

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3 files scannedscanner v1.2.0Oct 11, 2026

Content sha256 d5d0bc6ef29dff22… — run codexguild_scan_skills after installing to verify your local copy.

Static analysis is a first line of defense, not a guarantee. Read the source

SKILL.md

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Vitest Testing Skill

Core Patterns

Basic Test

import { describe, it, expect, vi, beforeEach } from 'vitest';
import { Calculator } from './calculator';

describe('Calculator', () => {
  let calc: Calculator;
  beforeEach(() => { calc = new Calculator(); });

  it('adds two numbers', () => {
    expect(calc.add(2, 3)).toBe(5);
  });

  it('throws on divide by zero', () => {
    expect(() => calc.divide(10, 0)).toThrow();
  });
});

Mocking (vi instead of jest)

import { vi } from 'vitest';

// Mock module
vi.mock('./database', () => ({
  getUser: vi.fn().mockResolvedValue({ name: 'Alice' }),
  saveUser: vi.fn().mockResolvedValue(true),
}));

// Mock function
const mockFn = vi.fn();
mockFn.mockReturnValue(42);
mockFn.mockResolvedValue({ data: 'test' });

// Spy
const spy = vi.spyOn(console, 'log').mockImplementation(() => {});
expect(spy).toHaveBeenCalledWith('message');
spy.mockRestore();

// Timers
vi.useFakeTimers();
vi.advanceTimersByTime(1000);
vi.runAllTimers();
vi.useRealTimers();

In-Source Testing

// src/math.ts — tests alongside code!
export function add(a: number, b: number) { return a + b; }
export function multiply(a: number, b: number) { return a * b; }

if (import.meta.vitest) {
  const { it, expect } = import.meta.vitest;
  it('adds', () => { expect(add(2, 3)).toBe(5); });
  it('multiplies', () => { expect(multiply(3, 4)).toBe(12); });
}

Snapshot Testing

it('serializes user', () => {
  expect(serializeUser(user)).toMatchSnapshot();
});

it('inline snapshot', () => {
  expect(serializeUser(user)).toMatchInlineSnapshot(`
    { "name": "Alice", "email": "alice@test.com" }
  `);
});

React Component Testing

import { render, screen } from '@testing-library/react';
import { describe, it, expect } from 'vitest';
import Button from './Button';

describe('Button', () => {
  it('renders with label', () => {
    render(<Button label="Click me" />);
    expect(screen.getByText('Click me')).toBeDefined();
  });
});

Anti-Patterns

BadGoodWhy
jest.fn()vi.fn()Vitest uses vi
jest.mock()vi.mock()Different namespace
No type safetyTypeScript + strictVitest is TS-first

Quick Reference

TaskCommand
Run oncenpx vitest run
Watchnpx vitest (default)
UInpx vitest --ui
Coveragenpx vitest --coverage
Specific filenpx vitest run src/math.test.ts
Filternpx vitest run -t "adds"

vitest.config.ts

import { defineConfig } from 'vitest/config';
export default defineConfig({
  test: {
    globals: true,
    environment: 'jsdom',
    coverage: { provider: 'v8', reporter: ['text', 'html'] },
    include: ['src/**/*.{test,spec}.{js,ts,tsx}'],
    includeSource: ['src/**/*.{js,ts}'],
  },
});

Deep Patterns → reference/playbook.md

§SectionLines
1Production ConfigurationConfig, workspace, setup file
2Mocking Patternsvi.mock, spies, timers, fetch
3React Testing LibraryComponents, hooks, providers
4Snapshot & Inline SnapshotsFile, inline, serializers
5Table-Driven Teststest.each, describe.each
6In-Source TestingCo-located tests in source
7API / Integration TestingServer tests with fetch
8CI/CD IntegrationGitHub Actions, scripts
9Debugging Quick-Reference10 common problems
10Best Practices Checklist13 items

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