Make sure that the UserName component displays the new username after successful form submission.

To ensure that the UserName component displays the new username after a successful form submission, you need to verify that the component's state updates correctly and the UI re-renders with the new value.

Example in React:

function UserName() {
  const [name, setName] = React.useState('');

  const handleSubmit = (e) => {
    e.preventDefault();
    const newName = e.target.elements.username.value;
    // simulate successful submission, e.g., API request
    setName(newName);
  };

  return (
    <div>
      <form onSubmit={handleSubmit}>
        <input name="username" type="text" />
        <button type="submit">Save</button>
      </form>
      <p>Username: {name}</p>
    </div>
  );
}

For testing, you can use React Testing Library to check that after submission, the DOM displays the new name:

import { render, screen, fireEvent } from '@testing-library/react';
import UserName from './UserName';

test('displays the new name after submission', () => {
  render(<UserName />);
  const input = screen.getByRole('textbox', { name: /username/i });
  const button = screen.getByRole('button', { name: /save/i });

  fireEvent.change(input, { target: { value: 'Ivan' } });
  fireEvent.click(button);

  expect(screen.getByText(/Username: Ivan/)).toBeInTheDocument();
});

Thus, it is verified that after a successful submission, the state updates and the component displays the new name.