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To migrate Jest tests in a Next.js project, first inventory what next/jest currently configures for you, then create a Vitest config that explicitly handles React, TypeScript path aliases, the DOM test environment, setup files, and any Next.js or asset mocks your tests need. Convert Jest APIs in a pilot slice, check differences in mock-reset behavior and module mocks, and expand only after the slice passes. Keep end-to-end coverage for async Server Components: the current Next.js Vitest guidance says Vitest does not support them.
1. Inventory the Jest setup before changing it
Do not start by replacing every jest. call. A Next.js project may rely on work that next/jest performed implicitly. Write down both the configuration and the behaviors your tests depend on.
- Configuration:
jest.config, options passed tonext/jest, setup files,moduleNameMapperentries, and any custom transformers or serializers. - Mocks and assets: root or package-level
__mocks__directories; mocks for CSS, images, fonts, and Next.js modules; and any code that depends on those mocks. - Test behavior: snapshots, fake timers, mock clearing or resetting, cleanup hooks, and tests that retain references to
mock.mock. - Execution: package scripts, CI commands, test file patterns, coverage exclusions, report formats, and thresholds.
next/jest supplies transforms and handling for CSS, images, fonts, environment loading, and .next exclusions. Vitest does not inherit those Jest-wrapper settings, so identify which ones the test suite actually uses and reproduce the necessary behavior deliberately.
2. Install the Vitest and React testing dependencies
The current Next.js App Router testing guide lists Vitest, the Vite React plugin, jsdom, React Testing Library, Testing Library DOM, and vite-tsconfig-paths when TypeScript path aliases are in use. Add the Jest DOM matchers package if your tests use those matchers.
#1 Best Overall
npm install -D vitest @vitejs/plugin-react jsdom @testing-library/react @testing-library/dom @testing-library/jest-dom vite-tsconfig-pathsUse the package manager and dependency conventions already used by the repository if it is not an npm project. Keep the installed Vitest and plugin versions compatible with the project rather than copying version numbers from an unrelated setup.
3. Add a root Vitest config and an explicit setup file
For a TypeScript project with React and path aliases, a minimal starting point is:
// vitest.config.ts
import { defineConfig } from 'vitest/config'
import react from '@vitejs/plugin-react'
import tsconfigPaths from 'vite-tsconfig-paths'
export default defineConfig({
plugins: [tsconfigPaths(), react()],
test: {
environment: 'jsdom',
setupFiles: ['./vitest.setup.ts'],
},
})Then add the setup file:
// vitest.setup.ts
import '@testing-library/jest-dom/vitest'jsdom provides browser-like APIs for DOM tests; it does not make every test a browser test. Use it for component and interaction tests that need a document. Tests that only exercise server-side or utility logic can use a non-DOM environment if the project benefits from separating them.
Rank #2
The vite-tsconfig-paths plugin makes TypeScript path aliases available to Vite’s resolver. If aliases were previously handled with Jest’s moduleNameMapper, verify representative imports rather than assuming the mapping is identical. Also review styles, static assets, fonts, and Next-specific modules: add explicit Vite handling or test mocks only for the imports your test suite needs. Keep these behaviors in configuration or setup files so failures are reproducible in CI.
Vitest does not enable Jest-style globals by default. The example therefore uses explicit imports in test files, such as import { describe, expect, it, vi } from 'vitest'. If the project opts into test.globals: true instead, account for global-dependent setup and cleanup behavior rather than mixing the two styles inconsistently.
4. Switch scripts and migrate a representative slice
Change the package scripts so developers can run tests interactively and CI can run them without watch mode:
{
"scripts": {
"test": "vitest",
"test:ci": "vitest run"
}
}Start with one representative unit or component-test folder, not the easiest test alone. Include examples that use aliases, Testing Library, snapshots, mocks, and any Next.js-specific imports. Resolve transform, environment, and module-resolution failures there before expanding to more folders.
Vitest aims to offer a Jest-compatible API, which makes many mechanical substitutions straightforward: jest.fn to vi.fn, jest.spyOn to vi.spyOn, and corresponding mock or timer APIs to their vi equivalents. Compatibility is not complete, however; review the behavior behind each substitution.
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| Jest behavior | What to verify in Vitest |
|---|---|
mockReset |
Jest resets a mock’s implementation to an empty function. Vitest resets it to its original implementation. Tests that expect a reset mock to return undefined may need an explicit implementation or a different reset strategy. |
| Module mock factories | Vitest factories should return an object containing the exports the module provides. Check named and default exports, and whether the test imports the same shape the factory returns. |
__mocks__ directories |
A root __mocks__ file is not loaded automatically just because it exists. Call vi.mock() where the module should be mocked, or configure the desired mock explicitly. |
| Mock and spy cleanup | Review the project’s use of clearMocks, resetMocks, and restoreMocks. Clearing call history, resetting an implementation, and restoring a spy are different operations; preserve the behavior the tests require. |
| Timers and stored mock state | Audit fake-timer setup and teardown, and code that saves a reference to mock.mock. Do not assume state references or cleanup behavior are interchangeable across runners. |
Keep isolation explicit. If globals are disabled, check whether Testing Library cleanup is being registered as expected; some auto-cleanup behavior depends on test-runner globals. A deliberate setup-file cleanup hook is preferable to relying on an accidental difference between environments.
Rank #4
6. Separate supported Next.js tests from async Server Component tests
The documented Vitest setup supports synchronous Server and Client Component unit tests. The Next.js guide states that Vitest currently does not support async Server Components because they are new to the React ecosystem. Cover those components with end-to-end tests rather than forcing them into the Vitest unit-test suite.
For other Next.js boundaries, use the inventory from the first step: if tests import a module whose behavior was previously supplied or masked by next/jest, provide the required transform, alias, or mock explicitly. Avoid mocking broadly just to make imports pass; mocks should preserve the behavior the test is intended to verify.
7. Re-establish coverage parity before enforcing a gate
Vitest supports V8 and Istanbul coverage providers. Run coverage with vitest --coverage or enable it through Vitest configuration, then compare the result with the Jest baseline before carrying over a CI threshold.
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- Compare line, branch, and function coverage rather than treating a single percentage as equivalent.
- Check report formats and confirm that CI or other tooling can consume the new reports.
- Reassess thresholds only after both runners are measuring the intended files consistently.
8. Stabilize CI, then remove Jest
Run vitest run in CI for a non-watch execution. If useful, run Jest and Vitest side by side temporarily to investigate differences in failures and coverage. Remove Jest dependencies and configuration only after the migrated suite’s behavior and reporting are understood and the required tests pass under Vitest.
There is no universal migration speedup percentage established by the official guidance. Compare runtime and flake rate in your own repository under comparable CI conditions; a faster runner is not a successful migration if it silently changes what the suite tests.
