Migration Guide

Migrating from Vitest 0.34.6

Minimum Requirements

Vitest 1.0 requires Vite 5.0 and Node.js 18 or higher.

All @vitest/* sub packages require Vitest version 1.0.

Snapshots Update #3961

Quotes in snapshots are no longer escaped, and all snapshots use backtick quotes (`) even if the string is just a single line.

1. Quotes are no longer escaped:

expect({ foo: 'bar' }).toMatchInlineSnapshot(`
  Object {
-    \\"foo\\": \\"bar\\",
+    "foo": "bar",
  }
`)

2. One-line snapshots now use "`" quotes instead of ':

- expect('some string').toMatchInlineSnapshot('"some string"')
+ expect('some string').toMatchInlineSnapshot(`"some string"`)

There were also changes to @vitest/snapshot package. If you are not using it directly, you don't need to change anything.

• You no longer need to extend SnapshotClient just to override equalityCheck method: just pass it down as isEqual when initiating an instance
• client.setTest was renamed to client.startCurrentRun
• client.resetCurrent was renamed to client.finishCurrentRun

Pools are Standardized #4172

We removed a lot of configuration options to make it easier to configure the runner to your needs. Please, have a look at migration examples if you rely on --threads or other related flags.

• --threads is now --pool=threads
• --no-threads is now --pool=forks
• --single-thread is now --poolOptions.threads.singleThread
• --experimental-vm-threads is now --pool=vmThreads
• --experimental-vm-worker-memory-limit is now --poolOptions.vmThreads.memoryLimit
• --isolate is now --poolOptions.<pool-name>.isolate and browser.isolate
• test.maxThreads is now test.poolOptions.<pool-name>.maxThreads
• test.minThreads is now test.poolOptions.<pool-name>.minThreads
• test.useAtomics is now test.poolOptions.<pool-name>.useAtomics
• test.poolMatchGlobs.child_process is now test.poolMatchGlobs.forks
• test.poolMatchGlobs.experimentalVmThreads is now test.poolMatchGlobs.vmThreads

{
  scripts: {
-    "test": "vitest --no-threads"
     // For identical behaviour:
+    "test": "vitest --pool forks --poolOptions.forks.singleFork"
     // Or multi parallel forks:
+    "test": "vitest --pool forks"

  }
}

{
  scripts: {
-    "test": "vitest --experimental-vm-threads"
+    "test": "vitest --pool vmThreads"
  }
}

{
  scripts: {
-    "test": "vitest --isolate false"
+    "test": "vitest --poolOptions.threads.isolate false"
  }
}

{
  scripts: {
-    "test": "vitest --no-threads --isolate false"
+    "test": "vitest --pool forks --poolOptions.forks.isolate false"
  }
}

Changes to Coverage #4265, #4442

Option coverage.all is now enabled by default. This means that all project files matching coverage.include pattern will be processed even if they are not executed.

Coverage thresholds API's shape was changed, and it now supports specifying thresholds for specific files using glob patterns:

export default defineConfig({
  test: {
    coverage: {
-      perFile: true,
-      thresholdAutoUpdate: true,
-      100: true,
-      lines: 100,
-      functions: 100,
-      branches: 100,
-      statements: 100,
+      thresholds: {
+        perFile: true,
+        autoUpdate: true,
+        100: true,
+        lines: 100,
+        functions: 100,
+        branches: 100,
+        statements: 100,
+      }
    }
  }
})

Mock Types #4400

A few types were removed in favor of Jest-style "Mock" naming.

- import { EnhancedSpy, SpyInstance } from 'vitest'
+ import { MockInstance } from 'vitest'

WARNING

SpyInstance is deprecated in favor of MockInstance and will be removed in the next major release.

Timer mocks #3925

vi.useFakeTimers() no longer automatically mocks process.nextTick. It's still possible to mock process.nextTick by explicitly specifying it by using vi.useFakeTimers({ toFake: ['nextTick'] }).

However, mocking process.nextTick is not possible when using --pool=forks. Use a different --pool option if you need process.nextTick mocking.

Migrating from Jest

Vitest has been designed with a Jest compatible API, in order to make the migration from Jest as simple as possible. Despite those efforts, you may still run into the following differences:

Globals as a Default

Jest has their globals API enabled by default. Vitest does not. You can either enable globals via the globals configuration setting or update your code to use imports from the vitest module instead.

If you decide to keep globals disabled, be aware that common libraries like testing-library will not run auto DOM cleanup.

Module Mocks

When mocking a module in Jest, the factory argument's return value is the default export. In Vitest, the factory argument has to return an object with each export explicitly defined. For example, the following jest.mock would have to be updated as follows:

jest.mock('./some-path', () => 'hello') 
vi.mock('./some-path', () => ({ 
  default: 'hello', 
})) 

For more details please refer to the vi.mock api section.

Auto-Mocking Behaviour

Unlike Jest, mocked modules in <root>/__mocks__ are not loaded unless vi.mock() is called. If you need them to be mocked in every test, like in Jest, you can mock them inside setupFiles.

Importing the Original of a Mocked Package

If you are only partially mocking a package, you might have previously used Jest's function requireActual. In Vitest, you should replace these calls with vi.importActual.

const { cloneDeep } = jest.requireActual('lodash/cloneDeep') 
const { cloneDeep } = await vi.importActual('lodash/cloneDeep') 

Accessing the Return Values of a Mocked Promise

Both Jest and Vitest store the results of all mock calls in the mock.results array, where the return values of each call are stored in the value property. However, when mocking or spying on a promise (e.g. using mockResolvedValue), in Jest the value property will be a promise, while in Vitest, it will become a resolved value when a promise is resolved.

await expect(spy.mock.results[0].value).resolves.toBe(123) 
expect(spy.mock.results[0].value).toBe(123) 

Envs

Just like Jest, Vitest sets NODE_ENV to test, if it wasn't set before. Vitest also has a counterpart for JEST_WORKER_ID called VITEST_POOL_ID (always less than or equal to maxThreads), so if you rely on it, don't forget to rename it. Vitest also exposes VITEST_WORKER_ID which is a unique ID of a running worker - this number is not affected by maxThreads, and will increase with each created worker.

Replace property

If you want to modify the object, you will use replaceProperty API in Jest, you can use vi.stubEnv or vi.spyOn to do the same also in Vitest.

Done Callback

From Vitest v0.10.0, the callback style of declaring tests is deprecated. You can rewrite them to use async/await functions, or use Promise to mimic the callback style.

it('should work', (done) => {
it('should work', () => new Promise(done => {
  // ...
  done()
})
}))

Hooks

beforeAll/beforeEach hooks may return teardown function in Vitest. Because of that you may need to rewrite your hooks declarations, if they return something other than undefined or null:

beforeEach(() => setActivePinia(createTestingPinia())) 
beforeEach(() => { setActivePinia(createTestingPinia()) }) 

In Jest hooks are called sequentially (one after another). By default, Vitest runs hooks in parallel. To use Jest's behavior, update sequence.hooks option:

export default defineConfig({
  test: {
    sequence: { 
      hooks: 'list', 
    } 
  }
})

Types

Vitest doesn't have an equivalent to jest namespace, so you will need to import types directly from vitest:

let fn: jest.Mock<string, [string]> 
import type { Mock } from 'vitest'
let fn: Mock<[string], string> 

Also, Vitest has Args type as a first argument instead of Returns, as you can see in diff.

Timers

Vitest doesn't support Jest's legacy timers.

Timeout

If you used jest.setTimeout, you would need to migrate to vi.setConfig:

jest.setTimeout(5_000) 
vi.setConfig({ testTimeout: 5_000 }) 

Vue Snapshots

This is not a Jest-specific feature, but if you previously were using Jest with vue-cli preset, you will need to install jest-serializer-vue package, and use it inside setupFiles:

vite.config.js

import {  } from 'vite'

export default ({
  : {
    : ['./tests/unit/setup.js']
  }
})

tests/unit/setup.js

import vueSnapshotSerializer from 'jest-serializer-vue'

expect.addSnapshotSerializer(vueSnapshotSerializer)

Otherwise your snapshots will have a lot of escaped " characters.