feat: Add UI for /stats slash command (#883)

packages/cli/src/ui/components/HistoryItemDisplay.test.tsx

@@ -0,0 +1,76 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { render } from 'ink-testing-library';
+import { describe, it, expect, vi } from 'vitest';
+import { HistoryItemDisplay } from './HistoryItemDisplay.js';
+import { HistoryItem, MessageType } from '../types.js';
+import { CumulativeStats } from '../contexts/SessionContext.js';
+
+// Mock child components
+vi.mock('./messages/ToolGroupMessage.js', () => ({
+  ToolGroupMessage: () => <div />,
+}));
+
+describe('<HistoryItemDisplay />', () => {
+  const baseItem = {
+    id: 1,
+    timestamp: 12345,
+    isPending: false,
+    availableTerminalHeight: 100,
+  };
+
+  it('renders UserMessage for "user" type', () => {
+    const item: HistoryItem = {
+      ...baseItem,
+      type: MessageType.USER,
+      text: 'Hello',
+    };
+    const { lastFrame } = render(
+      <HistoryItemDisplay {...baseItem} item={item} />,
+    );
+    expect(lastFrame()).toContain('Hello');
+  });
+
+  it('renders StatsDisplay for "stats" type', () => {
+    const stats: CumulativeStats = {
+      turnCount: 1,
+      promptTokenCount: 10,
+      candidatesTokenCount: 20,
+      totalTokenCount: 30,
+      cachedContentTokenCount: 5,
+      toolUsePromptTokenCount: 2,
+      thoughtsTokenCount: 3,
+      apiTimeMs: 123,
+    };
+    const item: HistoryItem = {
+      ...baseItem,
+      type: MessageType.STATS,
+      stats,
+      lastTurnStats: stats,
+      duration: '1s',
+    };
+    const { lastFrame } = render(
+      <HistoryItemDisplay {...baseItem} item={item} />,
+    );
+    expect(lastFrame()).toContain('Stats');
+  });
+
+  it('renders AboutBox for "about" type', () => {
+    const item: HistoryItem = {
+      ...baseItem,
+      type: MessageType.ABOUT,
+      cliVersion: '1.0.0',
+      osVersion: 'test-os',
+      sandboxEnv: 'test-env',
+      modelVersion: 'test-model',
+    };
+    const { lastFrame } = render(
+      <HistoryItemDisplay {...baseItem} item={item} />,
+    );
+    expect(lastFrame()).toContain('About Gemini CLI');
+  });
+});