React Testing Advanced

Advanced testing techniques.

Testing Custom Hooks

```javascript import { renderHook, act } from '@testing-library/react';

test('useCounter', () => { const { result } = renderHook(() => useCounter());

expect(result.current.count).toBe(0);

act(() => { result.current.increment(); });

expect(result.current.count).toBe(1); }); ```

Mocking API Calls

```javascript global.fetch = jest.fn(() => Promise.resolve({ json: () => Promise.resolve([{ id: 1, name: 'John' }]) }) );

test('fetches users', async () => { render(<Users />); const user = await screen.findByText('John'); expect(user).toBeInTheDocument(); }); ```

Testing Context

```javascript test('uses theme context', () => { render( <ThemeProvider> <ThemedButton /> </ThemeProvider> );

const button = screen.getByRole('button'); expect(button).toHaveClass('dark'); }); ```

Snapshot Testing

```javascript test('matches snapshot', () => { const { container } = render(<Button>Click</Button>); expect(container).toMatchSnapshot(); }); ```

Remember

- Test user behavior - Mock external dependencies - Use renderHook for hooks - Snapshot for UI changes

> Next: Learn micro-frontends!