1 files changed, 120 insertions, 0 deletions
diff --git a/packages/cli/src/ui/hooks/useTimer.test.ts b/packages/cli/src/ui/hooks/useTimer.test.ts
new file mode 100644
index 00000000..20d44d17
--- /dev/null
+++ b/packages/cli/src/ui/hooks/useTimer.test.ts
@@ -0,0 +1,120 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest';
+import { renderHook, act } from '@testing-library/react';
+import { useTimer } from './useTimer.js';
+
+describe('useTimer', () => {
+  beforeEach(() => {
+    vi.useFakeTimers();
+  });
+
+  afterEach(() => {
+    vi.restoreAllMocks();
+  });
+
+  it('should initialize with 0', () => {
+    const { result } = renderHook(() => useTimer(false, 0));
+    expect(result.current).toBe(0);
+  });
+
+  it('should not increment time if isActive is false', () => {
+    const { result } = renderHook(() => useTimer(false, 0));
+    act(() => {
+      vi.advanceTimersByTime(5000);
+    });
+    expect(result.current).toBe(0);
+  });
+
+  it('should increment time every second if isActive is true', () => {
+    const { result } = renderHook(() => useTimer(true, 0));
+    act(() => {
+      vi.advanceTimersByTime(1000);
+    });
+    expect(result.current).toBe(1);
+    act(() => {
+      vi.advanceTimersByTime(2000);
+    });
+    expect(result.current).toBe(3);
+  });
+
+  it('should reset to 0 and start incrementing when isActive becomes true from false', () => {
+    const { result, rerender } = renderHook(
+      ({ isActive, resetKey }) => useTimer(isActive, resetKey),
+      { initialProps: { isActive: false, resetKey: 0 } },
+    );
+    expect(result.current).toBe(0);
+
+    rerender({ isActive: true, resetKey: 0 });
+    expect(result.current).toBe(0); // Should reset to 0 upon becoming active
+
+    act(() => {
+      vi.advanceTimersByTime(1000);
+    });
+    expect(result.current).toBe(1);
+  });
+
+  it('should reset to 0 when resetKey changes while active', () => {
+    const { result, rerender } = renderHook(
+      ({ isActive, resetKey }) => useTimer(isActive, resetKey),
+      { initialProps: { isActive: true, resetKey: 0 } },
+    );
+    act(() => {
+      vi.advanceTimersByTime(3000); // 3s
+    });
+    expect(result.current).toBe(3);
+
+    rerender({ isActive: true, resetKey: 1 }); // Change resetKey
+    expect(result.current).toBe(0); // Should reset to 0
+
+    act(() => {
+      vi.advanceTimersByTime(1000);
+    });
+    expect(result.current).toBe(1); // Starts incrementing from 0
+  });
+
+  it('should be 0 if isActive is false, regardless of resetKey changes', () => {
+    const { result, rerender } = renderHook(
+      ({ isActive, resetKey }) => useTimer(isActive, resetKey),
+      { initialProps: { isActive: false, resetKey: 0 } },
+    );
+    expect(result.current).toBe(0);
+
+    rerender({ isActive: false, resetKey: 1 });
+    expect(result.current).toBe(0);
+  });
+
+  it('should clear timer on unmount', () => {
+    const { unmount } = renderHook(() => useTimer(true, 0));
+    const clearIntervalSpy = vi.spyOn(global, 'clearInterval');
+    unmount();
+    expect(clearIntervalSpy).toHaveBeenCalledOnce();
+  });
+
+  it('should preserve elapsedTime when isActive becomes false, and reset to 0 when it becomes active again', () => {
+    const { result, rerender } = renderHook(
+      ({ isActive, resetKey }) => useTimer(isActive, resetKey),
+      { initialProps: { isActive: true, resetKey: 0 } },
+    );
+
+    act(() => {
+      vi.advanceTimersByTime(3000); // Advance to 3 seconds
+    });
+    expect(result.current).toBe(3);
+
+    rerender({ isActive: false, resetKey: 0 });
+    expect(result.current).toBe(3); // Time should be preserved when timer becomes inactive
+
+    // Now make it active again, it should reset to 0
+    rerender({ isActive: true, resetKey: 0 });
+    expect(result.current).toBe(0);
+    act(() => {
+      vi.advanceTimersByTime(1000);
+    });
+    expect(result.current).toBe(1);
+  });
+});