jest-compat Layer

vitest-native/jest-compat lets an existing Jest suite run under Vitest without rewriting jest.* to vi.*. Your test files keep their jest calls and just work — it's an opt-in layer that clears the mechanical Jest-API coupling (not a full auto-migration).

Setup

// vitest.config.ts
import { defineConfig } from 'vitest/config'
import { reactNative } from 'vitest-native'
import { jestCompatAliases, jestCompatSetup, jestMockTransform } from 'vitest-native/jest-compat'

export default defineConfig({
  plugins: [reactNative({ engine: 'native' }), jestMockTransform()], // or engine: 'mock'
  resolve: {
    dedupe: ['react', 'react-test-renderer', 'react-is'],
    alias: { ...jestCompatAliases() },
  },
  test: {
    globals: true,
    environment: 'node',
    setupFiles: [jestCompatSetup],
  },
})

The three pieces

Piece	What it does
jestCompatSetup	Installs a jest global backed by Vitest's vi, so jest.fn / jest.spyOn / jest.useFakeTimers work unchanged. Adds the sync jest.requireActual / requireMock that Vitest only ships as async, a global require, and no-ops jest.setTimeout.
jestMockTransform()	A Vite plugin that makes top-level jest.mock(...) actually apply. Vitest only hoists vi.mock, so it rewrites jest.mock / unmock / doMock / doUnmock to the hoisted vi.* form, and runs each factory's return through Jest's CommonJS interop (so () => Component and named-only factories resolve the way Jest resolves them).
jestCompatAliases()	resolve.alias entries: @jest/globals → a Vitest-globals shim (unblocks @testing-library/react-native < 12), and @testing-library/jest-native/extend-expect → a no-op (those matchers are already registered).

You don't swap the test API

In your Jest test	Under jest-compat
jest.fn(), jest.spyOn(), jest.useFakeTimers()	work as-is (the global jest is vi)
import { jest } from '@jest/globals'	resolves to the vi-backed jest (aliased)
top-level jest.mock('m', factory)	hoisted + applied, with Jest's factory interop
describe / it / expect / beforeEach	same names, available as globals

What it does not do

It clears the API coupling, not the suite-specific work — you still:

• write mocks for native libraries with no preset,
• re-record snapshots (vitest -u),
• and fix the occasional factory that references an out-of-scope mock-prefixed variable (Jest's Babel plugin allows that; Vitest doesn't).

For the full migration walkthrough — including which manual mocks you can delete and how snapshots change — see Migrating from Jest.