---
url: /config/fakerandom.md
---

# fakeRandom  5.2.0 {#fakerandom}

* **Type:** `{ enableGlobally?: boolean }`

Options for [`vi.useFakeRandom()`](/api/vi#vi-usefakerandom).

## fakeRandom.enableGlobally

* **Type:** `boolean`
* **Default:** `false`

Should Vitest automatically call [`vi.useFakeRandom()`](/api/vi#vi-usefakerandom) before it imports the setup files and the test file. Then `Math.random`, `crypto` and `node:crypto` return values from the [`seed`](/config/seed) option in the whole file, also in libraries that keep a reference to these functions when they load, such as lodash and `uuid`.

```js [vitest.config.js]
import { defineConfig } from 'vitest/config'

export default defineConfig({
  test: {
    fakeRandom: {
      enableGlobally: true,
    },
  },
})
```

If a test calls [`vi.useRealRandom()`](/api/vi#vi-userealrandom), Vitest calls `vi.useFakeRandom()` again before the next test.

If the config does not set a [`seed`](/config/seed), each run gets new values. For values that must be the same on every run, for example IDs in a snapshot, set `seed` in the config.

A module keeps the functions that it found when it loaded. So a module that kept the fake functions still returns seeded values after `vi.useRealRandom()`. A module that loaded before Vitest imported the setup files, for example in a custom [environment](/config/environment), still returns real values. For other values that the fake cannot repeat, see [`vi.useFakeRandom`](/api/vi#vi-usefakerandom).

This option cannot be used together with [`restoreRandom`](/config/restorerandom).

::: warning
Tests and hooks that run at the same time (see [`test.concurrent`](/api/test#test-concurrent) and [`sequence.hooks`](/config/sequence#sequence-hooks)) share these functions, so their values would depend on the order of the calls. The fake functions throw an error in concurrent tests and suites, and in hooks that run at the same time. Use [`context.random`](/guide/test-context#random) in concurrent tests.
:::