Add component tests for document title, file browser, and layout switcher; update Vitest config to include component tests

Author: erdalkaraca

packages/core/test/components/document-title.test.ts

@@ -0,0 +1,52 @@
+// @vitest-environment jsdom
+import { beforeEach, describe, expect, it, vi } from 'vitest';
+
+const { activePartGet } = vi.hoisted(() => ({
+  activePartGet: vi.fn(),
+}));
+
+vi.mock('../../src/core/appstate', () => ({
+  activePartSignal: { get: () => activePartGet() },
+}));
+
+vi.mock('../../src/core/apploader', () => ({
+  appLoaderService: { getCurrentApp: vi.fn(() => null) },
+}));
+
+vi.mock('../../src/core/signals', () => ({
+  watchSignal: vi.fn(),
+}));
+
+vi.mock('../../src/core/i18n', () => ({
+  i18n: vi.fn(async () => ({ NO_PART: 'No part' })),
+}));
+
+describe('document-title (component helpers)', () => {
+  beforeEach(() => {
+    activePartGet.mockReset();
+  });
+
+  it('getActivePartDisplayName returns NO_PART when nothing is focused', async () => {
+    activePartGet.mockReturnValue(undefined);
+    const { getActivePartDisplayName } = await import('../../src/components/document-title');
+    expect(getActivePartDisplayName()).toBe('No part');
+  });
+
+  it('prefers tab contribution label when present', async () => {
+    activePartGet.mockReturnValue({
+      tabContribution: { label: 'Editor' },
+      getAttribute: () => null,
+    });
+    const { getActivePartDisplayName } = await import('../../src/components/document-title');
+    expect(getActivePartDisplayName()).toBe('Editor');
+  });
+
+  it('falls back to element id when label is missing', async () => {
+    activePartGet.mockReturnValue({
+      tabContribution: {},
+      getAttribute: (name: string) => (name === 'id' ? 'part-1' : null),
+    });
+    const { getActivePartDisplayName } = await import('../../src/components/document-title');
+    expect(getActivePartDisplayName()).toBe('part-1');
+  });
+});