Faking System Time using Jest Fake Timers and Luxon Settings

index.test.ts

import { Settings, DateTime } from 'luxon';
import { theFutureIsNow, theFutureIsNowWithLuxon } from './index';

describe("Fake Timer", () => {
    describe("Testing with Jest fake timers", () => {
        test('theFutureIsNow should return the time in two hours', () => {
            jest.useFakeTimers();
            jest.setSystemTime(new Date('2021-01-01T00:00:00Z').getTime());
            expect(theFutureIsNow()).toEqual(new Date('2021-01-01T02:00:00Z'));
        })
    })


    describe("Testing with Luxon Settings class", () => {
        Settings.now = () => new Date('2021-01-01T00:00:00Z').getTime()
        test('theFutureIsNowWithLuxon should return the time in two hours', () => {
            expect(theFutureIsNowWithLuxon().toISO({ suppressMilliseconds: true })).toEqual('2021-01-01T02:00:00Z');
        })
    })
})

index.ts

import { DateTime } from 'luxon'

/**
 * Adds two hours to the current time and returns the time.
 */
export function theFutureIsNow() {
    const now = new Date();
    now.setHours(now.getHours() + 2);
    return now;
}

/**
 * Adds two hours the the current time retrieved with Luxon and returns the time.
 */
export function theFutureIsNowWithLuxon() {
    return DateTime.utc().plus({ hours: 2 });
}