Not sure if it's working properly or I am noob

[erikkubica]

Hey,

I am trying to do some test for a calendar and I have noticed some weird things.

I have just checked what time it is now in Tokyo it said it's "Feb 14 03:15" so I have mocked Etc/GMT+9 and initialized the date object with "2023-02-14 03:15:00". To make sure, I have initialized it with the same date in browser to check if it initializes with my current timezone or not, it was correct, so the Tokyo time should be accurate.

I have tried to convert the timezone-mock date object with moment and Intl, but all of them return wrongly converted timezone.

So I have something easier. My local timezone is CET (GMT+1) so I have mocked that. Initialized the date with my local time string and run a conversion to Europe/Bratislava (yes, form +1 to +1) and result was +2 (from 19:15 -> 21:15) because 1+1 is 2 right? Wrong.

I have started digging and tried to change "const date = new Date("2023-02-14 03:15:00");" to "const date = new timezoneMock._Date("2023-02-14 03:15:00");" to access the original date object. The test result is correct.

So basically, something is not right with the mocked Date object, because while date-time conversion works with the native Date, it does not work properly with the mocked Date.

So basically I am unable to test if my code works properly if I cannot get a functioning Date object in a certain timezone.

 test("convertDateIntoTimeZone | Tokyo => Bratislava | Convert date into timezone", () => {
        timezoneMock.register("Etc/GMT+9");
        // Mon Feb 14 2023 19:15:00 GMT+0900
        const date = new Date("2023-02-14 03:15:00");

        // Bratislava is GMT+1
        // Output should be: Mon Feb 13 2023 19:15:00 GMT+0100
        // Double-checked with bing and google and other online tools
        const dateAsGMT1 = new Intl.DateTimeFormat("sv-SE", {
            day: "2-digit",
            month: "2-digit",
            year: "numeric",
            hour: "2-digit",
            minute: "2-digit",
            timeZone: "Europe/Bratislava", // GMT+1 / CET
            timeZoneName: "short",
        }).format(date);

        // Fails: Output is "2023-02-14 13:15 CET"
        expect(dateAsGMT1).toEqual("2023-02-13 19:15 CET");
        // Expected: "2023-02-13 19:15 CET"
        // Received: "2023-02-14 13:15 CET"

        timezoneMock.unregister();
    });

[Jimbly]

Not sure this only issue or not, but Tokyo should use Etc/GMT-9 timezone, see the note in the Readme, the Etc/GMT timezones are basically the opposite of what you'd expect. Since your output is off 18 hours from what you expect, that sounds likely to be the issue =)

[erikkubica]

@Jimbly thank you that slipped my eyes after a long day. Just out of curiosity, why does it work in the opposite way? Are you trying to punish humanity?

[Jimbly]

Heheh, not my decision, I also think it's terrible! We just pull the timezone names from the OS, and that's how the Etc timezones are defined I guess -_-. If you pass Etc/GMT+1 to Intl.DateTimeFormat in Node, you'll see it comes back as a GMT-1 date string too. Discussion about it here.