feat: add CartSnackbar component with tests

client/src/shared/ui/CartSnackbar.tsx

@@ -0,0 +1,46 @@
+import { useEffect } from 'react'
+import Alert from '@mui/material/Alert'
+import Button from '@mui/material/Button'
+import Snackbar from '@mui/material/Snackbar'
+import { useNavigate } from 'react-router-dom'
+import { useUnit } from 'effector-react'
+import { $cartSnackOpen, cartDismissed } from '@/shared/model/cart-notifications'
+
+export function CartSnackbar() {
+  const open = useUnit($cartSnackOpen)
+  const navigate = useNavigate()
+
+  useEffect(() => {
+    if (!open) return
+    const timer = setTimeout(() => cartDismissed(), 4000)
+    return () => clearTimeout(timer)
+  }, [open])
+
+  const handleClose = () => cartDismissed()
+
+  const handleGoToCart = () => {
+    cartDismissed()
+    navigate('/cart')
+  }
+
+  return (
+    <Snackbar
+      open={open}
+      onClose={handleClose}
+      anchorOrigin={{ vertical: 'bottom', horizontal: 'center' }}
+      autoHideDuration={4000}
+    >
+      <Alert
+        severity="success"
+        onClose={handleClose}
+        action={
+          <Button color="success" size="small" onClick={handleGoToCart}>
+            Перейти в корзину
+          </Button>
+        }
+      >
+        Товар добавлен в корзину
+      </Alert>
+    </Snackbar>
+  )
+}

client/src/shared/ui/__tests__/CartSnackbar.test.tsx

@@ -0,0 +1,55 @@
+import { render, screen, fireEvent, act } from '@testing-library/react'
+import { describe, it, expect, vi } from 'vitest'
+import { MemoryRouter } from 'react-router-dom'
+import { cartAdded, cartDismissed } from '@/shared/model/cart-notifications'
+import { CartSnackbar } from '@/shared/ui/CartSnackbar'
+
+function renderWithRouter() {
+  render(
+    <MemoryRouter>
+      <CartSnackbar />
+    </MemoryRouter>,
+  )
+}
+
+describe('CartSnackbar', () => {
+  it('is hidden when store is false', () => {
+    cartDismissed()
+    renderWithRouter()
+    expect(screen.queryByText(/товар добавлен/i)).not.toBeInTheDocument()
+  })
+
+  it('shows snackbar when cartAdded is fired', () => {
+    renderWithRouter()
+    cartAdded()
+    expect(screen.getByText(/товар добавлен/i)).toBeInTheDocument()
+    expect(screen.getByRole('button', { name: /перейти в корзину/i })).toBeInTheDocument()
+  })
+
+  it('closes on dismiss button click', () => {
+    renderWithRouter()
+    cartAdded()
+    const closeBtn = screen.getByLabelText(/закрыть/i)
+    fireEvent.click(closeBtn)
+    expect(screen.queryByText(/товар добавлен/i)).not.toBeInTheDocument()
+  })
+
+  it('auto-closes after 4 seconds', () => {
+    vi.useFakeTimers()
+    renderWithRouter()
+    cartAdded()
+    act(() => {
+      vi.advanceTimersByTime(4000)
+    })
+    expect(screen.queryByText(/товар добавлен/i)).not.toBeInTheDocument()
+    vi.useRealTimers()
+  })
+
+  it('navigates to /cart and closes on "Перейти в корзину" click', () => {
+    renderWithRouter()
+    cartAdded()
+    const goBtn = screen.getByRole('button', { name: /перейти в корзину/i })
+    fireEvent.click(goBtn)
+    expect(screen.queryByText(/товар добавлен/i)).not.toBeInTheDocument()
+  })
+})