feat(expiry): KST util — todayInKstString + nextKstMidnightMs (#5 v0.2.3)

tests/unit/kstDate.test.ts

@@ -0,0 +1,37 @@
+import { describe, it, expect } from 'vitest';
+import { todayInKstString, nextKstMidnightMs } from '@main/util/kstDate.js';
+
+describe('todayInKstString', () => {
+  it('returns KST calendar date as YYYY-MM-DD', () => {
+    // 2026-05-01 12:00 UTC = 2026-05-01 21:00 KST
+    expect(todayInKstString(new Date('2026-05-01T12:00:00Z'))).toBe('2026-05-01');
+  });
+
+  it('handles UTC→KST date rollover (UTC 23:30 → KST next day 08:30)', () => {
+    expect(todayInKstString(new Date('2026-05-01T23:30:00Z'))).toBe('2026-05-02');
+  });
+
+  it('handles KST midnight exactly (UTC 15:00 = KST 00:00 next day)', () => {
+    expect(todayInKstString(new Date('2026-05-01T15:00:00Z'))).toBe('2026-05-02');
+  });
+});
+
+describe('nextKstMidnightMs', () => {
+  it('returns the next KST 00:00 epoch ms (UTC 12:00 → +12h to KST midnight)', () => {
+    // 2026-05-01 12:00 UTC = 2026-05-01 21:00 KST → 다음 KST 자정 = 2026-05-02 00:00 KST
+    // = 2026-05-01 15:00 UTC
+    const now = Date.parse('2026-05-01T12:00:00Z');
+    const next = nextKstMidnightMs(now);
+    expect(new Date(next).toISOString()).toBe('2026-05-01T15:00:00.000Z');
+  });
+
+  it('returns 24h-from-now-ish when called shortly after KST midnight', () => {
+    // 2026-05-01 15:01 UTC = 2026-05-02 00:01 KST → 다음 KST 자정 = 2026-05-03 00:00 KST
+    // = 2026-05-02 15:00 UTC (≈ 23h59m later)
+    const now = Date.parse('2026-05-01T15:01:00Z');
+    const next = nextKstMidnightMs(now);
+    expect(new Date(next).toISOString()).toBe('2026-05-02T15:00:00.000Z');
+    expect(next - now).toBeGreaterThan(23 * 60 * 60 * 1000);
+    expect(next - now).toBeLessThan(24 * 60 * 60 * 1000);
+  });
+});