Setup

caution

jest-extended only supports Jest version 27.2.5 and newer. If you're using an older version of Jest, use 1.2.1.

Create a setup script with the following:

testSetup.js

// add all jest-extended matchers
import * as matchers from 'jest-extended';
expect.extend(matchers);

// or just add specific matchers
import { toBeArray, toBeSealed } from 'jest-extended';
expect.extend({ toBeArray, toBeSealed });

Add your setup script to your Jest setupFilesAfterEnv configuration. See for help

package.json

"jest": {
  "setupFilesAfterEnv": ["./testSetup.js"]
}

To automatically extend expect with all matchers, you can use

package.json

"jest": {
  "setupFilesAfterEnv": ["jest-extended/all"]
}

Use with vitest

jest-extended works with vitest because their expect.extend API is compatible. In your setup script:

testSetup.js

import { expect } from 'vitest';
import * as matchers from 'jest-extended';
expect.extend(matchers);

Add this setup script to your vitest.config.js:

vitest.config.js

export default defineConfig({
  test: {
    setupFiles: ['./testSetup.js'],
  },
});

Vitest TypeScript types setup

To use Vitest with TypeScript, create a file named jest-extended.d.ts with the content below in addition to the setup above.

/// <reference types="vitest" />

export interface CustomMatchers<R> extends Record<string, any> {
  toHaveBeenCalledAfter(
    mock: jest.MockInstance<any, any[]> | import('vitest').MockInstance<any, any[]>,
    failIfNoFirstInvocation?: boolean,
  ): R;

  toHaveBeenCalledBefore(
    mock: jest.MockInstance<any, any[]> | import('vitest').MockInstance<any, any[]>,
    failIfNoSecondInvocation?: boolean,
  ): R;

  toHaveBeenCalledExactlyOnceWith(...args: unknown[]): R;
}

For Vitest >= 0.31.0, append the content below to the new file.

declare module 'vitest' {
  // eslint-disable-next-line @typescript-eslint/no-empty-interface
  interface Assertion<T = any> extends CustomMatchers<T> {}
}

For Vitest < 0.31.0, append the content below to the new file.

declare namespace Vi {
  // eslint-disable-next-line @typescript-eslint/no-empty-interface
  interface AsymmetricMatchersContaining extends CustomMatchers<any> {}
}