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agent-skills/skills/vitest/references/features-context.md
Jason Woltje f5792c40be feat: Complete fleet — 94 skills across 10+ domains
Pulled ALL skills from 15 source repositories:
- anthropics/skills: 16 (docs, design, MCP, testing)
- obra/superpowers: 14 (TDD, debugging, agents, planning)
- coreyhaines31/marketingskills: 25 (marketing, CRO, SEO, growth)
- better-auth/skills: 5 (auth patterns)
- vercel-labs/agent-skills: 5 (React, design, Vercel)
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- Plus 13 individual skills from various repos

Mosaic Stack is not limited to coding — the Orchestrator and
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Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
2026-02-16 16:27:42 -06:00

4.3 KiB

name, description
name description
test-context-fixtures Test context, custom fixtures with test.extend

Test Context & Fixtures

Built-in Context

Every test receives context as first argument:

test('context', ({ task, expect, skip }) => {
  console.log(task.name)  // Test name
  expect(1).toBe(1)       // Context-bound expect
  skip()                  // Skip test dynamically
})

Context Properties

  • task - Test metadata (name, file, etc.)
  • expect - Expect bound to this test (important for concurrent tests)
  • skip(condition?, message?) - Skip the test
  • onTestFinished(fn) - Cleanup after test
  • onTestFailed(fn) - Run on failure only

Custom Fixtures with test.extend

Create reusable test utilities:

import { test as base } from 'vitest'

// Define fixture types
interface Fixtures {
  db: Database
  user: User
}

// Create extended test
export const test = base.extend<Fixtures>({
  // Fixture with setup/teardown
  db: async ({}, use) => {
    const db = await createDatabase()
    await use(db)           // Provide to test
    await db.close()        // Cleanup
  },
  
  // Fixture depending on another fixture
  user: async ({ db }, use) => {
    const user = await db.createUser({ name: 'Test' })
    await use(user)
    await db.deleteUser(user.id)
  },
})

Using fixtures:

test('query user', async ({ db, user }) => {
  const found = await db.findUser(user.id)
  expect(found).toEqual(user)
})

Fixture Initialization

Fixtures only initialize when accessed:

const test = base.extend({
  expensive: async ({}, use) => {
    console.log('initializing')  // Only runs if test uses it
    await use('value')
  },
})

test('no fixture', () => {})           // expensive not called
test('uses fixture', ({ expensive }) => {}) // expensive called

Auto Fixtures

Run fixture for every test:

const test = base.extend({
  setup: [
    async ({}, use) => {
      await globalSetup()
      await use()
      await globalTeardown()
    },
    { auto: true }  // Always run
  ],
})

Scoped Fixtures

File Scope

Initialize once per file:

const test = base.extend({
  connection: [
    async ({}, use) => {
      const conn = await connect()
      await use(conn)
      await conn.close()
    },
    { scope: 'file' }
  ],
})

Worker Scope

Initialize once per worker:

const test = base.extend({
  sharedResource: [
    async ({}, use) => {
      await use(globalResource)
    },
    { scope: 'worker' }
  ],
})

Injected Fixtures (from Config)

Override fixtures per project:

// test file
const test = base.extend({
  apiUrl: ['/default', { injected: true }],
})

// vitest.config.ts
defineConfig({
  test: {
    projects: [
      {
        test: {
          name: 'prod',
          provide: { apiUrl: 'https://api.prod.com' },
        },
      },
    ],
  },
})

Scoped Values per Suite

Override fixture for specific suite:

const test = base.extend({
  environment: 'development',
})

describe('production tests', () => {
  test.scoped({ environment: 'production' })
  
  test('uses production', ({ environment }) => {
    expect(environment).toBe('production')
  })
})

test('uses default', ({ environment }) => {
  expect(environment).toBe('development')
})

Extended Test Hooks

Type-aware hooks with fixtures:

const test = base.extend<{ db: Database }>({
  db: async ({}, use) => {
    const db = await createDb()
    await use(db)
    await db.close()
  },
})

// Hooks know about fixtures
test.beforeEach(({ db }) => {
  db.seed()
})

test.afterEach(({ db }) => {
  db.clear()
})

Composing Fixtures

Extend from another extended test:

// base-test.ts
export const test = base.extend<{ db: Database }>({
  db: async ({}, use) => { /* ... */ },
})

// admin-test.ts
import { test as dbTest } from './base-test'

export const test = dbTest.extend<{ admin: User }>({
  admin: async ({ db }, use) => {
    const admin = await db.createAdmin()
    await use(admin)
  },
})

Key Points

  • Use { } destructuring to access fixtures
  • Fixtures are lazy - only initialize when accessed
  • Return cleanup function from fixtures
  • Use { auto: true } for setup fixtures
  • Use { scope: 'file' } for expensive shared resources
  • Fixtures compose - extend from extended tests