feat: add unit tests and CI configuration

lib/hooks/__tests__/useOnlineStatus.test.ts

@@ -0,0 +1,34 @@
+import { describe, it, expect } from 'vitest'
+import { renderHook, act } from '@testing-library/react'
+import { useOnlineStatus } from '../useOnlineStatus'
+
+describe('useOnlineStatus', () => {
+  it('returns true initially', () => {
+    const { result } = renderHook(() => useOnlineStatus())
+    expect(result.current).toBe(true)
+  })
+
+  it('returns false when offline event fires', () => {
+    const { result } = renderHook(() => useOnlineStatus())
+
+    act(() => {
+      window.dispatchEvent(new Event('offline'))
+    })
+
+    expect(result.current).toBe(false)
+  })
+
+  it('returns true when online event fires after offline', () => {
+    const { result } = renderHook(() => useOnlineStatus())
+
+    act(() => {
+      window.dispatchEvent(new Event('offline'))
+    })
+    expect(result.current).toBe(false)
+
+    act(() => {
+      window.dispatchEvent(new Event('online'))
+    })
+    expect(result.current).toBe(true)
+  })
+})