What is the improvement or update you wish to see?

Styleheets and images aren't used in the tests but importing them may cause errors, so they will need to be mocked. Create the mock files referenced in the configuration above - fileMock.js and styleMock.js - inside a mocks directory:

In Testing documentation in sentence reffered above there is misspelling.

Is there any context that might help us understand?

The first word Styleheets is misspelled, it suppose to be Stylesheets.

Does the docs page already exist? Please link to it.

https://nextjs.org/docs/testing