Snapshot testing is a technique where the output of a React component is captured and stored in a file (called a snapshot).
Future test runs compare the component’s output to the stored snapshot to detect unexpected changes.

How it works:

• When you first run the test, a snapshot file is generated.
• If the component changes, the next test run will detect a difference and fail the test.
• Developers can review changes and update the snapshot if they are intentional.

Example with Jest:

import { render } from '@testing-library/react';
import Header from './Header';

test('matches snapshot', () => {
  const { asFragment } = render(<Header />);
  expect(asFragment()).toMatchSnapshot();
});

Benefits:

• Easy to detect unintended UI changes.
• Great for tracking visual or structural changes over time.

Caution:

• Snapshot tests can become noisy if overused.
• They should be reviewed carefully to avoid blindly updating snapshots without understanding the changes.

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