Vitest skill

Skill Pyfagorass/bookofspells/skills/lambdatest/vitest-skill

📖 The Book of Spells: a curated, enchanted index of real LLM tooling — and a pipeline that gathers SKILL.md skills from many houses into one searchable shelf.

Install

npx -y skills add Pyfagorass/bookofspells --skill vitest-skill

Assembled from the repository path, not quoted from the project. Check it against their README if it does not work.

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What its author says it does

Copied from the file, not written here

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".

The file declares its own license as MIT. That is the author’s claim about this one file, and it is not the same thing as the license GitHub reports for the repository, which is listed with the other numbers below.

SKILL.md

3.9 KB, as published. Nobody here has run it

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": "[email protected]" }
  `);
});

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

Bad	Good	Why
`jest.fn()`	`vi.fn()`	Vitest uses `vi`
`jest.mock()`	`vi.mock()`	Different namespace
No type safety	TypeScript + strict	Vitest is TS-first

Quick Reference

Task	Command
Run once	`npx vitest run`
Watch	`npx vitest` (default)
UI	`npx vitest --ui`
Coverage	`npx vitest --coverage`
Specific file	`npx vitest run src/math.test.ts`
Filter	`npx 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`

§	Section	Lines
1	Production Configuration	Config, workspace, setup file
2	Mocking Patterns	vi.mock, spies, timers, fetch
3	React Testing Library	Components, hooks, providers
4	Snapshot & Inline Snapshots	File, inline, serializers
5	Table-Driven Tests	test.each, describe.each
6	In-Source Testing	Co-located tests in source
7	API / Integration Testing	Server tests with fetch
8	CI/CD Integration	GitHub Actions, scripts
9	Debugging Quick-Reference	10 common problems
10	Best Practices Checklist	13 items