hidden-message.test.js

// __tests__/hidden-message.js
// these imports are something you'd normally configure Jest to import for you
// automatically. Learn more in the setup docs: https://testing-library.com/docs/react-testing-library/setup#cleanup
import '@testing-library/jest-dom'
// NOTE: jest-dom adds handy assertions to Jest and is recommended, but not required

import React from 'react'
import {render, fireEvent, screen} from '@testing-library/react'
import HiddenMessage from '../hidden-message'

test('shows the children when the checkbox is checked', () => {
  const testMessage = 'Test Message'
  render(<HiddenMessage>{testMessage}</HiddenMessage>)

  // query* functions will return the element or null if it cannot be found
  // get* functions will return the element or throw an error if it cannot be found
  expect(screen.queryByText(testMessage)).toBeNull()

  // the queries can accept a regex to make your selectors more resilient to content tweaks and changes.
  fireEvent.click(screen.getByLabelText(/show/i))

  // .toBeInTheDocument() is an assertion that comes from jest-dom
  // otherwise you could use .toBeDefined()
  expect(screen.getByText(testMessage)).toBeInTheDocument()
})