React Testing Library And Jest- The Complete Guide Apr 2026
act(() => result.current.increment() )
test('should increment counter', () => const result = renderHook(() => useCounter(0))
import userEvent from '@testing-library/user-event' test('form submission', async () => const user = userEvent.setup() render(<LoginForm />) React Testing Library and Jest- The Complete Guide
render(<Button onClick=handleClick>Click Me</Button>)
expect(result.current.count).toBe(1) ) Mock functions with Jest const mockFn = jest.fn() mockFn('hello') expect(mockFn).toHaveBeenCalledWith('hello') expect(mockFn).toHaveBeenCalledTimes(1) // Mock return value jest.fn().mockReturnValue('fixed value') jest.fn().mockResolvedValue('async value') jest.fn().mockImplementation(arg => arg * 2) Mock modules // Mock entire module jest.mock('../api', () => ( fetchUser: jest.fn(), )) // Mock with dynamic implementation jest.mock('axios', () => ( get: jest.fn(() => Promise.resolve( data: id: 1 )), )) Mock timers jest.useFakeTimers() test('delayed action', () => render(<DelayedComponent />) act(() => result
await user.click(button) expect(button).toHaveTextContent('ON')
expect(screen.getByText('Loading...')).toBeInTheDocument() const result = renderHook(() =>
act(() => jest.advanceTimersByTime(1000) )
// Don't use act directly (userEvent handles it) act(() => render(<Component />) )
