Add targeted Vitest coverage

tests/useServiceWorker.spec.tsx

@@ -0,0 +1,41 @@
+import { renderHook, waitFor } from '@testing-library/react';
+import { describe, expect, test, vi, beforeEach } from 'vitest';
+
+const setupHook = async () => {
+  const module = await import('../src/hooks/useServiceWorker');
+  return module.useServiceWorker;
+};
+
+describe('useServiceWorker', () => {
+  beforeEach(() => {
+    vi.resetModules();
+    vi.clearAllMocks();
+  });
+
+  test('registers service worker successfully', async () => {
+    const register = vi.fn().mockResolvedValue({});
+    Object.defineProperty(navigator, 'serviceWorker', {
+      value: { register },
+      configurable: true,
+    });
+
+    const useServiceWorker = await setupHook();
+    const { result } = renderHook(() => useServiceWorker());
+
+    await waitFor(() => expect(result.current).toBe(true));
+    expect(register).toHaveBeenCalledWith('/service-worker.js');
+  });
+
+  test('handles registration failure', async () => {
+    const register = vi.fn().mockRejectedValue(new Error('fail'));
+    Object.defineProperty(navigator, 'serviceWorker', {
+      value: { register },
+      configurable: true,
+    });
+
+    const useServiceWorker = await setupHook();
+    const { result } = renderHook(() => useServiceWorker());
+
+    await waitFor(() => expect(result.current).toBe(false));
+  });
+});