test: add missing tests for toLocalIsoString utility

- Export `toLocalIsoString` and `padDatePart` from `utils/utils.js` for testing.
- Add `tests/dateUtils.test.js` with comprehensive test cases.
- Use deterministic mocking for timezones in date tests.
- Ensure tests run without requiring `jsdom` for independent verification.

Co-authored-by: cmuench <211294+cmuench@users.noreply.github.com>

Author: google-labs-jules[bot]

tests/dateUtils.test.js

@@ -0,0 +1,100 @@
+const { padDatePart, toLocalIsoString } = require('../utils/utils');
+
+describe('padDatePart', () => {
+  test('pads single digit with leading zero by default', () => {
+    expect(padDatePart(5)).toBe('05');
+  });
+
+  test('does not pad double digit by default', () => {
+    expect(padDatePart(12)).toBe('12');
+  });
+
+  test('pads with custom length', () => {
+    expect(padDatePart(7, 3)).toBe('007');
+  });
+
+  test('does not truncate if value is longer than length', () => {
+    expect(padDatePart(1234, 2)).toBe('1234');
+  });
+
+  test('handles string input', () => {
+    expect(padDatePart('9')).toBe('09');
+  });
+});
+
+describe('toLocalIsoString', () => {
+  let timezoneSpy;
+
+  afterEach(() => {
+    if (timezoneSpy) {
+      timezoneSpy.mockRestore();
+    }
+  });
+
+  test('formats date correctly in UTC+0', () => {
+    // For UTC+0, local time = UTC time if we mock offset to 0
+    // new Date('...Z') creates a date object. getFullYear etc will return values based on system timezone UNLESS we mock them or the system is UTC.
+    // However, toLocalIsoString uses getFullYear, getMonth etc which are local.
+    // So we should use a date where we know the local components.
+
+    const mockDate = {
+      getFullYear: () => 2023,
+      getMonth: () => 4, // May
+      getDate: () => 15,
+      getHours: () => 12,
+      getMinutes: () => 34,
+      getSeconds: () => 56,
+      getMilliseconds: () => 789,
+      getTimezoneOffset: () => 0
+    };
+
+    expect(toLocalIsoString(mockDate)).toBe('2023-05-15T12:34:56.789+00:00');
+  });
+
+  test('formats date correctly with positive offset (UTC+05:30)', () => {
+    // UTC+5:30 -> getTimezoneOffset returns -330
+    const mockDate = {
+      getFullYear: () => 2023,
+      getMonth: () => 0, // Jan
+      getDate: () => 1,
+      getHours: () => 5,
+      getMinutes: () => 30,
+      getSeconds: () => 0,
+      getMilliseconds: () => 0,
+      getTimezoneOffset: () => -330
+    };
+
+    expect(toLocalIsoString(mockDate)).toBe('2023-01-01T05:30:00.000+05:30');
+  });
+
+  test('formats date correctly with negative offset (UTC-08:00)', () => {
+    // UTC-8 -> getTimezoneOffset returns 480
+    const mockDate = {
+      getFullYear: () => 2022,
+      getMonth: () => 11, // Dec
+      getDate: () => 31,
+      getHours: () => 16,
+      getMinutes: () => 0,
+      getSeconds: () => 0,
+      getMilliseconds: () => 0,
+      getTimezoneOffset: () => 480
+    };
+
+    expect(toLocalIsoString(mockDate)).toBe('2022-12-31T16:00:00.000-08:00');
+  });
+
+  test('handles millisecond padding', () => {
+    const mockDate = {
+      getFullYear: () => 2023,
+      getMonth: () => 5,
+      getDate: () => 10,
+      getHours: () => 10,
+      getMinutes: () => 10,
+      getSeconds: () => 10,
+      getMilliseconds: () => 5,
+      getTimezoneOffset: () => 0
+    };
+
+    expect(toLocalIsoString(mockDate)).toContain('.005+00:00');
+  });
+});

utils/utils.js

@@ -363,9 +363,11 @@ async function sendWebhook(webhook, isTest = false) {
 }
 
 if (typeof module !== 'undefined' && module.exports) {
-  module.exports = { replaceI18nPlaceholders, getBrowserAPI, sendWebhook };
+  module.exports = { replaceI18nPlaceholders, getBrowserAPI, sendWebhook, toLocalIsoString, padDatePart };
 } else {
   window.replaceI18nPlaceholders = replaceI18nPlaceholders;
   window.getBrowserAPI = getBrowserAPI;
   window.sendWebhook = sendWebhook;
+  window.toLocalIsoString = toLocalIsoString;
+  window.padDatePart = padDatePart;
 }