code: public static Clock fixed(Instant fixedInstant, ZoneId zone) {
          Objects.requireNonNull(fixedInstant, "fixedInstant");
          Objects.requireNonNull(zone, "zone");
          return new FixedClock(fixedInstant, zone);
      }
docs: Obtains a clock that always returns the same instant.
  <p>
  This clock simply returns the specified instant.
  As such, it is not a clock in the conventional sense.
  The main use case for this is in testing, where the fixed clock ensures
  tests are not dependent on the current clock.
  <p>
  The returned implementation is immutable, thread-safe and {@code Serializable}.
  
  @param fixedInstant  the instant to use as the clock, not null
  @param zone  the time-zone to use to convert the instant to date-time, not null
  @return a clock that always returns the same instant, not null