Vitest Testing

Vitest testing framework patterns and best practices. Use when writing unit tests, integration tests, configuring vitest.config, mocking with vi.mock/vi.fn,...

Security Scan

This is a documentation/instruction-only skill about Vitest testing patterns; its files and runtime instructions are consistent with the stated purpose and request no credentials or installs, though provenance is unspecified.

Purpose & Capability

Name/description match the provided files: examples, config snippets, mocking and pattern guidance for Vitest. No unrelated binaries, credentials, or third-party services are requested.

Instruction Scope

SKILL.md and companion files contain sample test code, config examples, and mocking patterns. They do not instruct reading arbitrary host files, exfiltrating data, or contacting external endpoints. They do show process.env/.env.test usage as normal examples for tests.

Install Mechanism

No install spec and no code files that would be written to disk or executed by an installer. This is instruction-only, the lowest install risk.

Credentials

The documentation shows how tests can access environment variables (process.env, .env.test and vi.stubEnv) but the skill does not declare or require any environment variables or credentials. Examples referencing env vars are expected for testing docs but users should avoid putting secrets into test env files.

Persistence & Privilege

always is false, no config paths or persistent modification of other skills or system settings. The skill is user-invocable and may be invoked by agents normally, which is expected for instructional skills.

Assessment

This skill is a set of Vitest examples and best-practice notes and appears coherent with its stated purpose. It's low-risk because it requests no credentials and has no installer, but two practical cautions: (1) provenance is unspecified (no homepage/source) — prefer content from an official or known author when security/trust matters; (2) the docs show using environment variables and setup files: do not place secrets in test env files or automatically run untrusted test setup code in CI or on machines with access to sensitive data. If you need stronger assurance, ask the publisher for a source repository or license before installing/using.

Vitest Best Practices

Quick Reference

import { describe, it, expect, beforeEach, vi } from 'vitest'

describe('feature name', () => {
  beforeEach(() => {
    vi.clearAllMocks()
  })

  it('should do something specific', () => {
    expect(actual).toBe(expected)
  })

  it.todo('planned test')
  it.skip('temporarily disabled')
  it.only('run only this during dev')
})

Common Assertions

// Equality
expect(value).toBe(42)                    // Strict (===)
expect(obj).toEqual({ a: 1 })             // Deep equality
expect(obj).toStrictEqual({ a: 1 })       // Strict deep (checks types)

// Truthiness
expect(value).toBeTruthy()
expect(value).toBeFalsy()
expect(value).toBeNull()
expect(value).toBeUndefined()

// Numbers
expect(0.1 + 0.2).toBeCloseTo(0.3)
expect(value).toBeGreaterThan(5)

// Strings/Arrays
expect(str).toMatch(/pattern/)
expect(str).toContain('substring')
expect(array).toContain(item)
expect(array).toHaveLength(3)

// Objects
expect(obj).toHaveProperty('key')
expect(obj).toHaveProperty('nested.key', 'value')
expect(obj).toMatchObject({ subset: 'of properties' })

// Exceptions
expect(() => fn()).toThrow()
expect(() => fn()).toThrow('error message')
expect(() => fn()).toThrow(/pattern/)

Async Testing

// Async/await (preferred)
it('fetches data', async () => {
  const data = await fetchData()
  expect(data).toEqual({ id: 1 })
})

// Promise matchers - ALWAYS await these
await expect(fetchData()).resolves.toEqual({ id: 1 })
await expect(fetchData()).rejects.toThrow('Error')

// Wrong - creates false positive
expect(promise).resolves.toBe(value)  // Missing await!

Quick Mock Reference

const mockFn = vi.fn()
mockFn.mockReturnValue(42)
mockFn.mockResolvedValue({ data: 'value' })

expect(mockFn).toHaveBeenCalled()
expect(mockFn).toHaveBeenCalledWith('arg1', 'arg2')
expect(mockFn).toHaveBeenCalledTimes(2)

Additional Documentation

• Mocking: See references/mocking.md for module mocking, spying, cleanup
• Configuration: See references/config.md for vitest.config, setup files, coverage
• Patterns: See references/patterns.md for timers, snapshots, anti-patterns

Test Methods Quick Reference

Method	Purpose
it() / test()	Define test
describe()	Group tests
beforeEach() / afterEach()	Per-test hooks
beforeAll() / afterAll()	Per-suite hooks
.skip	Skip test/suite
.only	Run only this
.todo	Placeholder
.concurrent	Parallel execution
.each([...])	Parameterized tests