static bool expectTimeJump(double secondsToWait, O onMessage) {
  long diff = now()-sysNow();
  long start = sysNow();
  while (elapsedSeconds(start) < secondsToWait) {
    sleep(500);
    long diff2 = now()-sysNow()-diff;
    if (abs(diff2) > 100) {
      logQuotedWithDate(timeJumpLog(), diff2 + " ms");
      ret true with callF(onMessage, "Slept " + formatDouble(toSeconds(diff2), 1) + " seconds!");
    }
  }
  ret false with callF(onMessage, "No time jump occurred in " + secondsToWait + " seconds");
}