/vitest

Configuration

Vitest reads configuration from vitest.config.ts or vite.config.ts. It shares the same config format as Vite.

Basic Setup

// vitest.config.ts
import { defineConfig } from 'vitest/config'

export default defineConfig({
  test: {
    // test options
  },
})

Using with Existing Vite Config

Add Vitest types reference and use the test property:

// vite.config.ts
/// <reference types="vitest/config" />
import { defineConfig } from 'vite'

export default defineConfig({
  test: {
    globals: true,
    environment: 'jsdom',
  },
})

Merging Configs

If you have separate config files, use mergeConfig:

// vitest.config.ts
import { defineConfig, mergeConfig } from 'vitest/config'
import viteConfig from './vite.config'

export default mergeConfig(viteConfig, defineConfig({
  test: {
    environment: 'jsdom',
  },
}))

Common Options

defineConfig({
  test: {
    // Enable global APIs (describe, it, expect) without imports
    globals: true,
    
    // Test environment: 'node', 'jsdom', 'happy-dom'
    environment: 'node',
    
    // Setup files to run before each test file
    setupFiles: ['./tests/setup.ts'],
    
    // Include patterns for test files
    include: ['**/*.{test,spec}.{js,ts,jsx,tsx}'],
    
    // Exclude patterns
    exclude: ['**/node_modules/**', '**/dist/**'],
    
    // Limit test discovery to a directory (faster than broad excludes)
    dir: './src',

    // Test timeout in ms
    testTimeout: 5000,
    
    // Hook timeout in ms
    hookTimeout: 10000,
    
    // Coverage configuration (v4+: define `include`, no more `all`)
    coverage: {
      provider: 'v8', // or 'istanbul'
      reporter: ['text', 'html'],
      include: ['src/**/*.ts'],
    },
    
    // Run each file in an isolated module graph (threads/forks pools only)
    isolate: true,
    
    // Pool: 'forks' (default), 'threads', 'vmForks', 'vmThreads'
    pool: 'forks',
    
    // v4+: pool options are top-level (poolOptions was removed)
    maxWorkers: 4,
    fileParallelism: true,
    
    // Clear mock call history before each test (v5: defaults to true)
    clearMocks: true,
    
    // Restore spies created with vi.spyOn between tests
    restoreMocks: true,
    
    // Retry failed tests
    retry: 0,
    
    // Stop after first failure
    bail: 0,

    // v5: repeat every test N times regardless of result (flaky-hunting)
    repeats: 0,
  },
})

v5 Performance Config

defineConfig({
  test: {
    // Persist transformed modules on disk, reused across reruns AND separate
    // processes (stable in v5; was experimental.fsModuleCache). Cache lives in
    // node_modules by default; clear with `vitest --clearCache`. Not for browser.
    fsModuleCache: true,

    // Inline projects that don't change the Vite config reuse the declaring
    // config's Vite server (default true) — shared files transformed once.
    // Set false if a plugin must be re-instantiated per project.
    sharedViteServer: true,

    // Inject CJS globals (module/exports/require/__filename/__dirname) into
    // every module (default true). Set false for stricter ESM-like scope.
    injectCjsGlobals: false,

    // Detect async resources leaking past a test file (slow; debugging only)
    detectAsyncLeaks: false,
  },
})

v4/v5 Config Changes

• v5 requires Vite >= 6.4.0 and Node >= 22.12.0. vite is now a required peer dependency (Yarn users must yarn add -D vite).
• clearMocks defaults to true in v5 — vi.clearAllMocks() runs before every test (history cleared, implementations kept). Set clearMocks: false for the old behavior.
• Inline projects inherit the root config by default (extends defaults to true) — including Vite plugins/resolve.alias. Set extends: false to opt out. See advanced-projects.
• testNamePattern (-t) matches the >-joined full name ('math > adds'), not the space-joined Jest form.
• vi.mock/vi.unmock/vi.hoisted must be at the top level — nested calls now throw (they were only warned before).
• Pool default is forks (child processes), not threads.
• poolOptions removed — maxThreads/maxForks are now top-level maxWorkers; singleThread/singleFork become maxWorkers: 1, isolate: false; VM memoryLimit is vmMemoryLimit. minWorkers was removed.
• workspace removed — use projects. vitest.workspace.ts no longer supported.
• coverage.all and coverage.extensions removed — by default only covered files are reported; set coverage.include explicitly.
• Simplified exclude — only node_modules/.git excluded by default. Use test.dir to scope discovery, or spread configDefaults.exclude.
• Config not looked up from parent dirs — pass --config explicitly when running from a subdirectory.
• .vitest artifact dir — blob reports (.vitest/blob/), attachments (.vitest/attachments/), and the html/json/junit reporters now all live under a single .vitest/ directory; add one entry to .gitignore.
• test.sequential/describe.sequential/sequential removed — use { concurrent: false }.
• deps.optimizer.web renamed to deps.optimizer.client; deps.inline/deps.external moved under server.deps.

Conditional Configuration

Use mode or process.env.VITEST for test-specific config:

export default defineConfig(({ mode }) => ({
  plugins: mode === 'test' ? [] : [myPlugin()],
  test: {
    // test options
  },
}))

Projects (Monorepos)

Run different configurations in the same Vitest process:

defineConfig({
  test: {
    projects: [
      'packages/*',
      {
        test: {
          name: 'unit',
          include: ['tests/unit/**/*.test.ts'],
          environment: 'node',
        },
      },
      {
        test: {
          name: 'integration',
          include: ['tests/integration/**/*.test.ts'],
          environment: 'jsdom',
        },
      },
    ],
  },
})

Key Points

• Vitest uses Vite's transformation pipeline - same resolve.alias, plugins work
• vitest.config.ts takes priority over vite.config.ts
• Use --config flag to specify a custom config path (required from subdirectories in v5)
• process.env.VITEST is set to true when running tests
• Test config uses test property, rest is Vite config
• v5 requires Vite >= 6.4.0 and Node >= 22.12.0; vite is a required peer dependency