TypeError: expect.extend is not a function

[cseas]

I'm trying to add @testing-library/jest-dom to a project that uses both chai and jest. The global expect is aliased to chai.expect and jest's expect is available as jestExpect.

const jestExpect = global.expect;
global.expect = chai.expect;
global.jestExpect = jestExpect;

• @testing-library/jest-dom version: 5.15.0
• node version: v12.22.6
• npm (or yarn) version: yarn 1.22.11

What you did:

The default import doesn't work: import '@testing-library/jest-dom';
Using it emits the error: TypeError: expect.extend is not a function

So I tried importing the matchers separately and adding them to jestExpect manually.

import { toHaveTextContent } from '@testing-library/jest-dom';
jestExpect.extend({ toHaveTextContent });

But the same error still shows up even in the named import.

Suggested solution:

Importing '@testing-library/jest-dom' directly sets up matchers for global expect and that's okay but we should be able to individually import the matchers and assign them to an aliased jest expect as I tried to do above. The only other option to add these custom matchers looks like we'd need to migrate the entire codebase from chai to jest and that'd require a huge effort.

[cseas]

Update:

After looking at the source code, I was able to make it work. Just needed to change the import path to the matchers file.

import { toHaveTextContent } from '@testing-library/jest-dom/matchers';
jestExpect.extend({ toHaveTextContent });