feat(shopping): formatQuantity-Utility

src/lib/quantity-format.ts

@@ -0,0 +1,7 @@
+export function formatQuantity(q: number | null): string {
+	if (q === null || q === undefined) return '';
+	const rounded = Math.round(q);
+	if (Math.abs(q - rounded) < 0.01) return String(rounded);
+	// auf max. 2 Nachkommastellen, trailing Nullen raus
+	return q.toFixed(2).replace(/\.?0+$/, '');
+}

tests/unit/quantity-format.test.ts

@@ -0,0 +1,28 @@
+import { describe, it, expect } from 'vitest';
+import { formatQuantity } from '../../src/lib/quantity-format';
+
+describe('formatQuantity', () => {
+	it('renders null as empty string', () => {
+		expect(formatQuantity(null)).toBe('');
+	});
+
+	it('renders whole numbers as integer', () => {
+		expect(formatQuantity(400)).toBe('400');
+	});
+
+	it('renders near-integer as integer (epsilon 0.01)', () => {
+		expect(formatQuantity(400.001)).toBe('400');
+		expect(formatQuantity(399.999)).toBe('400');
+	});
+
+	it('renders fractional with up to 2 decimals, trailing zeros trimmed', () => {
+		expect(formatQuantity(0.5)).toBe('0.5');
+		expect(formatQuantity(0.333333)).toBe('0.33');
+		expect(formatQuantity(1.1)).toBe('1.1');
+		expect(formatQuantity(1.1)).toBe('1.1');
+	});
+
+	it('handles zero', () => {
+		expect(formatQuantity(0)).toBe('0');
+	});
+});