import userEvent from '@testing-library/user-event'

const { queryByTestId } = render(<App />);
const increaseButton = queryByTestId('increase-button');
userEvent.click(increaseButton)

const result = queryByTestId('result');
expect(result.textContent).toBe('1');

// JavaScript
const [result, setResult] = useState(0);

// HTML
<button data-testid="increase-button" onClick={() => setResult(result+1)}>+1</button>