test(time):asserted integer output for sub-second precision inputs

Signed-off-by: Himanshujha7 <tigmanshujah@gmail.com>

Author: Himanshujha7

utils/time.test.ts

@@ -63,6 +63,13 @@ describe('getSecondsUntilUTCMidnight', () => {
 
     expect(getSecondsUntilUTCMidnight()).toBe(64800); // 18 hours = 64800 s
   });
+
+  it('always returns an integer with sub-second precision input', () => {
+    vi.setSystemTime(new Date('2024-06-15T23:59:59.999Z'));
+
+    expect(Number.isInteger(getSecondsUntilUTCMidnight())).toBe(true);
+  });
+
 });
 
 it('returns positive seconds for every hour of day', () => {
@@ -145,6 +152,13 @@ describe('getSecondsUntilMidnightInTimezone', () => {
     }
   });
 
+  it('always returns an integer with sub-second precision input', () => {
+  // 2024-06-16T03:59:59.999Z is 23:59:59.999 in Etc/GMT+4 (UTC-4)
+    vi.setSystemTime(new Date('2024-06-16T03:59:59.999Z'));
+
+    expect(Number.isInteger(getSecondsUntilMidnightInTimezone('Etc/GMT+4'))).toBe(true);
+  });
+
   it('handles extreme timezone Etc/GMT-14 (UTC+14)', () => {
     // UTC 00:00 → local time 14:00 in UTC+14
     vi.setSystemTime(new Date('2024-06-15T00:00:00.000Z'));