code: public static ZonedDateTime randomZonedDateTimeBefore(ZonedDateTime before) {
      checkArgument(before != null, "Before must be non-null");
      Instant instant = randomInstantBefore(before.toInstant());
      return ZonedDateTime.ofInstant(instant, UTC);
    }
docs: Returns a random {@link ZonedDateTime} that is before the given {@link ZonedDateTime}.
  
  @param before the value that returned {@link ZonedDateTime} must be before
  @return the random {@link ZonedDateTime}
  @throws IllegalArgumentException if before is null or if before is equal to or before {@link
  RandomDateUtils#MIN_INSTANT}