test(shared): cover BackButton and OverflowPillButton

BackButton: visible vs aria-only label branches, custom class
application, history.back() click handler.

OverflowPillButton: +N pill render, aria-expanded matrix
(closed default → open after click), per-person link rendering with
correct href, Escape closes the dropdown.

Both are reused widely; their coverage closes the line and function gap
left after the DocumentTopBar split inflated the denominator.

Refs #496.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/lib/shared/primitives/BackButton.svelte.test.ts

@@ -0,0 +1,50 @@
+import { describe, it, expect, vi, afterEach } from 'vitest';
+import { cleanup, render } from 'vitest-browser-svelte';
+import { page } from 'vitest/browser';
+import BackButton from './BackButton.svelte';
+
+afterEach(cleanup);
+
+describe('BackButton', () => {
+	it('renders the visible label by default (showLabel=true)', async () => {
+		render(BackButton, { props: {} });
+
+		await expect.element(page.getByRole('button', { name: /^zurück$/i })).toBeVisible();
+	});
+
+	it('hides the visible label when showLabel is false', async () => {
+		render(BackButton, { props: { showLabel: false } });
+
+		const btn = (await page.getByRole('button').element()) as HTMLButtonElement;
+		// The label is exposed via aria-label only when showLabel=false.
+		expect(btn.getAttribute('aria-label')).toBe('Zurück');
+		expect(btn.textContent?.trim()).toBe('');
+	});
+
+	it('does not set an aria-label when the visible label is shown', async () => {
+		render(BackButton, { props: { showLabel: true } });
+
+		const btn = (await page.getByRole('button').element()) as HTMLButtonElement;
+		expect(btn.getAttribute('aria-label')).toBeNull();
+	});
+
+	it('applies the supplied class string to the button', async () => {
+		render(BackButton, { props: { class: 'custom-class' } });
+
+		const btn = (await page.getByRole('button').element()) as HTMLButtonElement;
+		expect(btn.classList.contains('custom-class')).toBe(true);
+	});
+
+	it('calls history.back() when clicked', async () => {
+		const backSpy = vi.spyOn(globalThis.history, 'back').mockImplementation(() => {});
+		try {
+			render(BackButton, { props: {} });
+
+			await page.getByRole('button').click();
+
+			expect(backSpy).toHaveBeenCalledOnce();
+		} finally {
+			backSpy.mockRestore();
+		}
+	});
+});

frontend/src/lib/shared/primitives/OverflowPillButton.svelte.test.ts

@@ -0,0 +1,61 @@
+import { describe, it, expect, afterEach } from 'vitest';
+import { cleanup, render } from 'vitest-browser-svelte';
+import { page } from 'vitest/browser';
+import OverflowPillButton from './OverflowPillButton.svelte';
+
+afterEach(cleanup);
+
+const persons = [
+	{ id: 'p1', firstName: 'Anna', lastName: 'Schmidt', displayName: 'Anna Schmidt' },
+	{ id: 'p2', firstName: 'Bert', lastName: 'Meier', displayName: 'Bert Meier' }
+];
+
+describe('OverflowPillButton', () => {
+	it('renders the +N pill labelled with the count', async () => {
+		render(OverflowPillButton, { props: { extraCount: 3, persons } });
+
+		await expect.element(page.getByText(/\+3/)).toBeVisible();
+	});
+
+	it('starts with aria-expanded=false', async () => {
+		render(OverflowPillButton, { props: { extraCount: 2, persons } });
+
+		await expect
+			.element(page.getByRole('button', { name: /weitere empfänger/i }))
+			.toHaveAttribute('aria-expanded', 'false');
+	});
+
+	it('opens the dropdown when the pill is clicked', async () => {
+		render(OverflowPillButton, { props: { extraCount: 2, persons } });
+
+		await page.getByRole('button', { name: /weitere empfänger/i }).click();
+
+		await expect
+			.element(page.getByRole('button', { name: /weitere empfänger/i }))
+			.toHaveAttribute('aria-expanded', 'true');
+	});
+
+	it('renders one link per person inside the open dropdown', async () => {
+		render(OverflowPillButton, { props: { extraCount: 2, persons } });
+
+		await page.getByRole('button', { name: /weitere empfänger/i }).click();
+
+		await expect
+			.element(page.getByRole('link', { name: 'Anna Schmidt' }))
+			.toHaveAttribute('href', '/persons/p1');
+		await expect
+			.element(page.getByRole('link', { name: 'Bert Meier' }))
+			.toHaveAttribute('href', '/persons/p2');
+	});
+
+	it('closes the dropdown when Escape is pressed', async () => {
+		render(OverflowPillButton, { props: { extraCount: 2, persons } });
+
+		const btn = page.getByRole('button', { name: /weitere empfänger/i });
+		await btn.click();
+		const btnEl = (await btn.element()) as HTMLButtonElement;
+		btnEl.dispatchEvent(new KeyboardEvent('keydown', { key: 'Escape', bubbles: true }));
+
+		await expect.element(btn).toHaveAttribute('aria-expanded', 'false');
+	});
+});