Edit

Example

Preact Testing Library works with both Preact Hooks and Classes. Your tests will be the same however you write your components.

Component

function HiddenMessage({ children }) {
  const [showMessage, setShowMessage] = useState(false)

  return (
    <div>
      <label htmlFor="toggle">Show Message</label>
      <input
        id="toggle"
        type="checkbox"
        onChange={e => setShowMessage(e.target.checked)}
        checked={showMessage}
      />
      {showMessage ? children : null}
    </div>
  )
}

Test

// NOTE: jest-dom adds handy assertions to Jest and it is recommended, but not required.
import '@testing-library/jest-dom/extend-expect'

import { h } from 'preact'
import { render, fireEvent } from '@testing-library/preact'

import HiddenMessage from '../hidden-message'

test('shows the children when the checkbox is checked', () => {
  const testMessage = 'Test Message'

  const { queryByText, getByLabelText, getByText } = 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(queryByText(testMessage)).toBeNull()

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

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