/vitest

Test API

Basic Test

import { expect, test } from 'vitest'

test('adds numbers', () => {
  expect(1 + 1).toBe(2)
})

// Alias: it
import { it } from 'vitest'

it('works the same', () => {
  expect(true).toBe(true)
})

Async Tests

test('async test', async () => {
  const result = await fetchData()
  expect(result).toBeDefined()
})

// Promises are automatically awaited
test('returns promise', () => {
  return fetchData().then(result => {
    expect(result).toBeDefined()
  })
})

Test Options

// Timeout (default: 5000ms)
test('slow test', async () => {
  // ...
}, 10_000)

// Or with options object
test('with options', { timeout: 10_000, retry: 2 }, async () => {
  // ...
})

Test Modifiers

Skip Tests

test.skip('skipped test', () => {
  // Won't run
})

// Conditional skip
test.skipIf(process.env.CI)('not in CI', () => {})
test.runIf(process.env.CI)('only in CI', () => {})

// Dynamic skip via context
test('dynamic skip', ({ skip }) => {
  skip(someCondition, 'reason')
  // ...
})

Focus Tests

test.only('only this runs', () => {
  // Other tests in file are skipped
})

Todo Tests

test.todo('implement later')

test.todo('with body', () => {
  // Not run, shows in report
})

Failing Tests

test.fails('expected to fail', () => {
  expect(1).toBe(2) // Test passes because assertion fails
})

Concurrent Tests

// Run tests in parallel
test.concurrent('test 1', async ({ expect }) => {
  // Use context.expect for concurrent tests
  expect(await fetch1()).toBe('result')
})

test.concurrent('test 2', async ({ expect }) => {
  expect(await fetch2()).toBe('result')
})

Opt Out of Concurrency

test.sequential was removed in v5. Use concurrent: false to opt a test out of inherited or globally configured concurrency:

test('must run alone', { concurrent: false }, async () => {})

Parameterized Tests

test.each

test.each([
  [1, 1, 2],
  [1, 2, 3],
  [2, 1, 3],
])('add(%i, %i) = %i', (a, b, expected) => {
  expect(a + b).toBe(expected)
})

// With objects
test.each([
  { a: 1, b: 1, expected: 2 },
  { a: 1, b: 2, expected: 3 },
])('add($a, $b) = $expected', ({ a, b, expected }) => {
  expect(a + b).toBe(expected)
})

// Template literal
test.each`
  a    | b    | expected
  ${1} | ${1} | ${2}
  ${1} | ${2} | ${3}
`('add($a, $b) = $expected', ({ a, b, expected }) => {
  expect(a + b).toBe(expected)
})

test.for

Preferred over .each - doesn't spread arrays:

test.for([
  [1, 1, 2],
  [1, 2, 3],
])('add(%i, %i) = %i', ([a, b, expected], { expect }) => {
  // Second arg is TestContext
  expect(a + b).toBe(expected)
})

v5: titles are formatted with pretty-format, and a string interpolated through a $ placeholder is no longer quoted (case $id → case a1, not case 'a1'). Interpolated-value length is capped by taskTitleValueFormatTruncate (default 40).

Test Context

First argument provides context utilities:

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

// signal (3.2+): AbortSignal aborted on timeout/cancel/bail
test('aborts on timeout', async ({ signal }) => {
  await fetch('/resource', { signal })
}, 2000)

// annotate (3.2+): attach notes shown by the reporter
test('annotated', async ({ annotate }) => {
  await annotate('see issue #123', 'issues')
})

Custom Test with Fixtures

Prefer the builder pattern (4.1+) for automatic type inference:

import { test as base } from 'vitest'

const test = base
  .extend('db', async ({}, { onCleanup }) => {
    const db = await createDb()
    onCleanup(() => db.close()) // runs after the test/scope
    return db
  })

test('query', async ({ db }) => {
  const users = await db.query('SELECT * FROM users')
  expect(users).toBeDefined()
})

See features-context for fixture scopes, test.override, and the Playwright-compatible object syntax.

Retry Configuration

test('flaky test', { retry: 3 }, async () => {
  // Retries up to 3 times on failure
})

// Advanced retry options
test('with delay', {
  retry: {
    count: 3,
    delay: 1000,
    condition: /timeout/i, // Only retry on timeout errors
  },
}, async () => {})

Tags

Tags must be declared in config first, then applied to tests (4.1+):

test('database test', { tags: ['db', 'slow'] }, async () => {})

// Run with a tag expression:
// vitest --tagsFilter "db && !flaky"

See features-test-tags for defining tags and filter syntax.

Benchmarks (v5)

bench is no longer a top-level import — it is a test-context fixture used inside test():

// file must match benchmark.include (e.g. *.bench.ts)
test('sort', async ({ bench }) => {
  await bench('Array.sort', () => [3, 1, 2].sort()).run()
})

Key Points

• Pass options as the second argument; the 3rd-arg options object was removed in v4 (a trailing timeout number is still allowed)
• Tests with no body are marked as todo
• test.only throws in CI unless allowOnly: true
• Use context's expect for concurrent tests and snapshots
• Function name is used as test name if passed as first arg
• test.sequential was removed in v5 — use { concurrent: false }