👀 Views: 64 💬 Answers: 1 📅 Created: 2025-06-21

jest testing dates JavaScript

I've searched everywhere and can't find a clear answer. I'm optimizing some code but I've tried everything I can think of but I tried several approaches but none seem to work. I'm trying to test a function that manipulates dates by adding days, but I'm running into issues because of timezone differences. My function works fine in the application, which is in UTC, but when I run the tests, they unexpected result due to differences in local timezone settings. Here's the function I'm trying to test: ```javascript function addDays(date, days) { const result = new Date(date); result.setUTCDate(result.getUTCDate() + days); return result; } ``` And here’s my test case using Jest: ```javascript test('adds 5 days to the date', () => { const date = new Date('2023-10-01T00:00:00Z'); const expectedDate = new Date('2023-10-06T00:00:00Z'); expect(addDays(date, 5)).toEqual(expectedDate); }); ``` When I run this test, I get an unexpected result because my local timezone is UTC+5 and it's affecting how dates are compared. The behavior message I'm seeing is: ``` Expected: 2023-10-06T00:00:00.000Z Received: 2023-10-05T19:00:00.000Z ``` I've tried adjusting the expected date to account for local time, but that feels wrong since it’s not how the function should ideally behave. I also contemplated using `toISOString()` when comparing the dates, but that doesn’t seem to resolve the underlying scenario either. Is there a best practice for testing date manipulation functions in JavaScript, especially when dealing with timezones? How can I ensure that my tests remain reliable regardless of the local timezone settings? For context: I'm using Javascript on macOS. What am I doing wrong? I'm working on a desktop app that needs to handle this. How would you solve this? For reference, this is a production desktop app. Is there a better approach?