function assertRelativeDateMs(date, expectedMs) {
  var actualMs = date.valueOf();
  var localOffset = date.getTimezoneOffset() * 60000;

  if (actualMs - localOffset !== expectedMs) {
    $ERROR(
      'Expected ' + date + ' to be ' + expectedMs +
      ' milliseconds from the Unix epoch'
    );
  }
}
@param {Date} date
@param {Number} expectedMs