@Override
        long now() {
            long present = now[nowIndex++];
            if (present == 0L) {
                // defensive coding against the innards of TimeTracker
                throw new IllegalStateException("0 is an unsupported time stamp value.");
            }
            return present;
        }
Check sanity of TimeTracker and ElapsedTime.

@author Steinar Knutsen
container-search/src/test/java/com/yahoo/search/statistics/ElapsedTimeTestCase.java