sinon-clock-tick-dst-fix.js

const _ = require('moment')

const MAX_MONTHS_TO_TEST_DST_OFFSET = 12;

const convertToMoment = (date) {
  if (date instanceof moment) return date;
  return new moment(date);
}

const wasDSTNowNot = (was, now = new moment()) => {
  return DateHelper.convertToMoment(was).isDST() && !now.isDST();
}

const wasNotDSTNowIs = (was, now = new moment()) => {
  return !DateHelper.convertToMoment(was).isDST() && now.isDST();
}

/**
  * Returns the duration of daylight savings time (DST) for the moment's timezone
  * @param {object} m moment
  * @return {number} a duration in minutes
  */
const durationDSTMins = m => {
  const isDST = m_ => m_.isDST();
  const isNotDST = m_ => !m_.isDST();
  const utcOffsetOfOpposite = (m, oppositeCond) => {
    let monthCounter = 1;
    while (monthCounter <= MAX_MONTHS_TO_TEST_DST_OFFSET) {
      const mNextMonth = new moment().add(monthCounter, 'month');
      if (oppositeCond(mNextMonth)) return mNextMonth.utcOffset();
      ++monthCounter;
    }
    return 0;
  };
  const calcDurationDSTMins = m => {
    if (isDST(m) && utcOffsetOfOpposite(m, isNotDST)) {
      return m.utcOffset() - utcOffsetOfOpposite(m, isNotDST);
    }
    if (utcOffsetOfOpposite(m, isDST)) {
      return m.utcOffset() - utcOffsetOfOpposite(m, isDST);
    }
    return 0;
  };
  return Math.abs(calcDurationDSTMins(m));
}

/*
 * Work around for sinon.fsinon.useFakeTimers().tick(ms) where new date ticking to crossing over
 * a date that DST starts or ends.
 * e.g. At the start of DST. the sinon clock might try and tick forward 7 hours in duration but
 * it actually only moves 6 relative hours because the clock gets wound back an hour.
 * So:
 *   if was DST --> now not DST, add DST duration worth of MS; or
 *   if was not DST --> now DST, subtract DST duration worth of MS
 */
sinonClockTick = (clock, msToTick) => {
  const mClockDate = new moment(clock.Date());
  const mClockDateToTickTo = new moment(mClockDate).add(
    msToTick,
    'milliseconds'
  );
  if (wasDSTNowNot(mClockDate, mClockDateToTickTo)) {
    mClockDateToTickTo.add(
      durationDSTMins(mClockDateToTickTo),
      'minutes'
    );
  } else if (wasNotDSTNowIs(mClockDate, mClockDateToTickTo)) {
    mClockDateToTickTo.subtract(
      durationDSTMins(mClockDateToTickTo),
      'minutes'
    );
  }
  const msToTickDSTAware = mClockDateToTickTo.diff(
    mClockDate,
    'milliseconds'
  );
  clock.tick(msToTickDSTAware);
}