How to start testing a NextJS app with Jest?

[OnkelTem]

Summary

I have a NextJS app with pages, not AppRouter.
Now I need to test one of the pages.

The official docs from here https://nextjs.org/docs/app/building-your-application/testing/jest suggest this code:

import '@testing-library/jest-dom'
import { render, screen } from '@testing-library/react'
import Page from '../app/page'
 
describe('Page', () => {
  it('renders a heading', () => {
    render(<Page />)
 
    const heading = screen.getByRole('heading', { level: 1 })
 
    expect(heading).toBeInTheDocument()
  })
})

which is completely missing the src/_app.tsx. So what's the point? How to perform a regular render run with next/jest?

Additional information

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Example

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