test(DateInput): add Vitest specs for DateInput component and date utils

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

frontend/src/lib/utils/date.spec.ts

@@ -0,0 +1,109 @@
+import { describe, expect, it } from 'vitest';
+import { formatGermanDateInput, isoToGerman, germanToIso } from './date';
+
+// ─── isoToGerman ─────────────────────────────────────────────────────────────
+
+describe('isoToGerman', () => {
+	it('converts a valid ISO date to DD.MM.YYYY', () => {
+		expect(isoToGerman('2024-12-20')).toBe('20.12.2024');
+	});
+
+	it('returns empty string for empty input', () => {
+		expect(isoToGerman('')).toBe('');
+	});
+
+	it('returns empty string for invalid format', () => {
+		expect(isoToGerman('not-a-date')).toBe('');
+	});
+});
+
+// ─── germanToIso ─────────────────────────────────────────────────────────────
+
+describe('germanToIso', () => {
+	it('converts DD.MM.YYYY to ISO', () => {
+		expect(germanToIso('20.12.2024')).toBe('2024-12-20');
+	});
+
+	it('returns empty string for partial input', () => {
+		expect(germanToIso('20.12')).toBe('');
+	});
+
+	it('returns empty string for empty input', () => {
+		expect(germanToIso('')).toBe('');
+	});
+});
+
+// ─── formatGermanDateInput ────────────────────────────────────────────────────
+
+describe('formatGermanDateInput – digit stream (no dots typed)', () => {
+	it('leaves 1–2 digits as-is', () => {
+		expect(formatGermanDateInput('2')).toBe('2');
+		expect(formatGermanDateInput('20')).toBe('20');
+	});
+
+	it('auto-inserts dot after 2 digits for 3–4 digit input', () => {
+		expect(formatGermanDateInput('201')).toBe('20.1');
+		expect(formatGermanDateInput('2012')).toBe('20.12');
+	});
+
+	it('auto-inserts two dots for 5–8 digit input', () => {
+		expect(formatGermanDateInput('20121')).toBe('20.12.1');
+		expect(formatGermanDateInput('20122024')).toBe('20.12.2024');
+	});
+
+	it('ignores digits beyond 8', () => {
+		expect(formatGermanDateInput('201220249')).toBe('20.12.2024');
+	});
+});
+
+describe('formatGermanDateInput – manual dot entry with padding', () => {
+	it('pads single-digit day to 2 digits when dot is typed after it', () => {
+		expect(formatGermanDateInput('3.')).toBe('03.');
+	});
+
+	it('does not pad a 2-digit day', () => {
+		expect(formatGermanDateInput('03.')).toBe('03.');
+		expect(formatGermanDateInput('20.')).toBe('20.');
+	});
+
+	it('pads single-digit month to 2 digits when dot is typed after it', () => {
+		expect(formatGermanDateInput('03.3.')).toBe('03.03.');
+	});
+
+	it('does not pad a 2-digit month', () => {
+		expect(formatGermanDateInput('03.12.')).toBe('03.12.');
+	});
+
+	it('pads both day and month in a fully typed date', () => {
+		expect(formatGermanDateInput('3.3.2012')).toBe('03.03.2012');
+	});
+
+	it('pads only day when month is already 2 digits', () => {
+		expect(formatGermanDateInput('3.12.2024')).toBe('03.12.2024');
+	});
+
+	it('pads only month when day is already 2 digits', () => {
+		expect(formatGermanDateInput('20.3.2024')).toBe('20.03.2024');
+	});
+
+	it('handles a complete date entered with manual dots and no padding needed', () => {
+		expect(formatGermanDateInput('20.12.2024')).toBe('20.12.2024');
+	});
+
+	it('overflows excess day digits into month when dot follows', () => {
+		expect(formatGermanDateInput('123.')).toBe('12.3');
+	});
+
+	it('caps year digits at 4', () => {
+		expect(formatGermanDateInput('03.03.20249')).toBe('03.03.2024');
+	});
+
+	it('overflows excess month digits into year (digit stream then continue typing)', () => {
+		// User typed digits → auto-dot gave "20.12", then types "2" → raw becomes "20.122"
+		expect(formatGermanDateInput('20.122')).toBe('20.12.2');
+	});
+
+	it('continues building year after overflow', () => {
+		expect(formatGermanDateInput('20.12.2024')).toBe('20.12.2024');
+	});
+});