diff --git a/frontend/src/lib/components/AnnotationSidePanel.svelte.spec.ts b/frontend/src/lib/components/AnnotationSidePanel.svelte.spec.ts
new file mode 100644
index 00000000..84745470
--- /dev/null
+++ b/frontend/src/lib/components/AnnotationSidePanel.svelte.spec.ts
@@ -0,0 +1,76 @@
+import { describe, it, expect, vi, afterEach } from 'vitest';
+import { cleanup, render } from 'vitest-browser-svelte';
+import { page } from 'vitest/browser';
+import AnnotationSidePanel from './AnnotationSidePanel.svelte';
+
+afterEach(() => {
+	cleanup();
+	vi.restoreAllMocks();
+});
+
+vi.stubGlobal(
+	'fetch',
+	vi.fn().mockResolvedValue({
+		ok: true,
+		json: async () => []
+	})
+);
+
+const baseProps = {
+	documentId: 'doc-1',
+	activeAnnotationPage: 1,
+	canComment: true,
+	currentUserId: 'user-1',
+	canAdmin: false,
+	onClose: vi.fn()
+};
+
+describe('AnnotationSidePanel – visibility', () => {
+	it('is hidden (translated off-screen) when activeAnnotationId is null', async () => {
+		render(AnnotationSidePanel, { ...baseProps, activeAnnotationId: null });
+		const panel = document.querySelector('[data-testid="annotation-side-panel"]');
+		expect(panel?.classList.contains('translate-x-full')).toBe(true);
+		expect(panel?.classList.contains('translate-x-0')).toBe(false);
+	});
+
+	it('is visible when activeAnnotationId is set', async () => {
+		render(AnnotationSidePanel, { ...baseProps, activeAnnotationId: 'ann-1' });
+		const panel = document.querySelector('[data-testid="annotation-side-panel"]');
+		expect(panel?.classList.contains('translate-x-0')).toBe(true);
+		expect(panel?.classList.contains('translate-x-full')).toBe(false);
+	});
+});
+
+describe('AnnotationSidePanel – close button', () => {
+	it('calls onClose when the close button is clicked', async () => {
+		const onClose = vi.fn();
+		render(AnnotationSidePanel, { ...baseProps, activeAnnotationId: 'ann-1', onClose });
+		await page.getByRole('button', { name: /schließen/i }).click();
+		expect(onClose).toHaveBeenCalledOnce();
+	});
+});
+
+describe('AnnotationSidePanel – targetCommentId forwarding', () => {
+	it('renders CommentThread when annotation is active', async () => {
+		render(AnnotationSidePanel, {
+			...baseProps,
+			activeAnnotationId: 'ann-1',
+			targetCommentId: 'comment-42'
+		});
+		// CommentThread renders inside the panel when activeAnnotationId is set
+		const panel = document.querySelector('[data-testid="annotation-side-panel"]');
+		expect(panel).not.toBeNull();
+		expect(panel?.classList.contains('translate-x-0')).toBe(true);
+	});
+
+	it('does not render CommentThread when annotation is null', async () => {
+		render(AnnotationSidePanel, {
+			...baseProps,
+			activeAnnotationId: null,
+			targetCommentId: 'comment-42'
+		});
+		// Panel is hidden and no fetch should have been triggered for comments
+		const panel = document.querySelector('[data-testid="annotation-side-panel"]');
+		expect(panel?.classList.contains('translate-x-full')).toBe(true);
+	});
+});
diff --git a/frontend/src/lib/utils/mention.spec.ts b/frontend/src/lib/utils/mention.spec.ts
index 301cbabe..5a7982be 100644
--- a/frontend/src/lib/utils/mention.spec.ts
+++ b/frontend/src/lib/utils/mention.spec.ts
@@ -96,6 +96,7 @@ describe('renderBody', () => {
 		const mentions: MentionDTO[] = [{ id: 'uuid-1', firstName: 'Hans', lastName: 'Müller' }];
 		const result = renderBody('Hey @Hans Müller!', mentions);
 		expect(result).toContain('<span');
+		expect(result).toContain('class="mention"');
 		expect(result).toContain('Hans Müller');
 	});
 
diff --git a/frontend/src/routes/layout.svelte.spec.ts b/frontend/src/routes/layout.svelte.spec.ts
index 6103089c..5729843a 100644
--- a/frontend/src/routes/layout.svelte.spec.ts
+++ b/frontend/src/routes/layout.svelte.spec.ts
@@ -1,8 +1,10 @@
-import { afterEach, describe, expect, it } from 'vitest';
+import { afterEach, describe, expect, it, vi } from 'vitest';
 import { cleanup, render } from 'vitest-browser-svelte';
 import { page, userEvent } from 'vitest/browser';
 import { createRawSnippet } from 'svelte';
 
+vi.mock('$env/static/public', () => ({ PUBLIC_NOTIFICATION_POLL_MS: '60000' }));
+
 afterEach(cleanup);
 
 const emptySnippet = createRawSnippet(() => ({ render: () => '<span></span>' }));