isRunningInTest()

isRunningInTest() returns true when the code looks like it runs under a test runner.

Signature

function isRunningInTest(): boolean

Parameters

None.

Behavior

It returns true when the first of these checks passes, in this order:

1. globalThis.window is not set, as in Node.js.
2. globalThis.EdgeRuntime is set.
3. Vitest’s __vitest_browser__ or __vitest_worker__ global is set.
4. window.navigator.userAgent contains StorybookTestRunner, jsdom, HappyDOM, or HeadlessChrome.

Otherwise it returns false.

Edge cases:

• Any context without window counts as a test. It returns true in every Node.js process, not only test runs.
• In a regular desktop browser, it returns false unless one of the globals above is set.
• In a headless Chrome session that is not a test, it returns true, because the user agent contains HeadlessChrome.

Use it in code that runs in a browser, such as a Storybook story, to tell a test run from a person viewing the page.

Examples

Under Vitest, in Node.js and in Vitest browser mode (both covered by the package’s tests):

import { isRunningInTest } from '@repobuddy/test'
import { expect, it } from 'vitest'

it('detects the code is running in test runner directly', () => {
  expect(isRunningInTest()).toBe(true)
})

Outside any test runner, in a plain Node.js script, it still returns true, because there is no window:

// check.mjs, run with `node check.mjs`
import { isRunningInTest } from '@repobuddy/test'

console.log(isRunningInTest()) // true

With a window whose user agent is a regular Chrome string, and none of the globals set, it returns false.

Related

• API