feat(cli): Allow custom title in CLI header (#706)

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

@@ -0,0 +1,48 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { render } from 'ink-testing-library';
+import { Header } from './Header.js';
+import { vi } from 'vitest';
+
+// Mock ink-gradient and ink-big-text as they might have complex rendering
+vi.mock('ink-gradient', () => ({
+  default: vi.fn(({ children }) => children), // Pass through children
+}));
+
+import { Text } from 'ink'; // Import the actual Text component from Ink
+
+vi.mock('ink-big-text', () => ({
+  default: vi.fn(({ text }) => <Text>{text}</Text>), // Use Ink's Text component
+}));
+
+describe('<Header />', () => {
+  it('should render with the default title "GEMINI" when no title prop is provided', () => {
+    const { lastFrame } = render(<Header />);
+    const output = lastFrame();
+    // Check if the output contains the default text "GEMINI"
+    // The actual output will be simple text due to mocking
+    expect(output).toContain('GEMINI');
+  });
+
+  it('should render with a custom title when the title prop is provided', () => {
+    const customTitle = 'My Custom CLI';
+    const { lastFrame } = render(<Header title={customTitle} />);
+    const output = lastFrame();
+    // Check if the output contains the custom title
+    expect(output).toContain(customTitle);
+  });
+
+  it('should render with an empty title if an empty string is provided', () => {
+    const customTitle = '';
+    const { lastFrame } = render(<Header title={customTitle} />);
+    const output = lastFrame();
+    // Depending on how BigText handles empty strings,
+    // it might render nothing or a specific representation.
+    // For this test, we'll assume it renders the empty string.
+    expect(output).toContain(''); // or check for a specific structure if BigText behaves differently
+  });
+});