fix(ui): elapsed time for scans

Signed-off-by: Deluan <deluan@navidrome.org>

ui/src/layout/useScanElapsedTime.test.jsx

@@ -0,0 +1,50 @@
+import { renderHook, act } from '@testing-library/react-hooks'
+import { vi } from 'vitest'
+import { useScanElapsedTime } from './useScanElapsedTime'
+
+describe('useScanElapsedTime', () => {
+  beforeEach(() => {
+    vi.useFakeTimers()
+  })
+
+  afterEach(() => {
+    vi.useRealTimers()
+  })
+
+  it('increments elapsed time while scanning', () => {
+    const { result } = renderHook(
+      ({ scanning, elapsed }) => useScanElapsedTime(scanning, elapsed),
+      {
+        initialProps: { scanning: true, elapsed: 0 },
+      },
+    )
+
+    act(() => {
+      vi.advanceTimersByTime(3000)
+    })
+
+    expect(result.current).toBe(3e9)
+  })
+
+  it('stops incrementing when not scanning', () => {
+    const { result, rerender } = renderHook(
+      ({ scanning, elapsed }) => useScanElapsedTime(scanning, elapsed),
+      {
+        initialProps: { scanning: false, elapsed: 2e9 },
+      },
+    )
+
+    act(() => {
+      vi.advanceTimersByTime(2000)
+    })
+
+    expect(result.current).toBe(2e9)
+
+    rerender({ scanning: true, elapsed: 2e9 })
+    act(() => {
+      vi.advanceTimersByTime(1000)
+    })
+
+    expect(result.current).toBe(3e9)
+  })
+})