public TimestampOffset entry(int n) {
        return maybeLock(lock, () -> {
            if (n >= entries())
                throw new IllegalArgumentException("Attempt to fetch the " + n + "th entry from time index "
                    + file().getAbsolutePath() + " which has size " + entries());
            return parseEntry(mmap(), n);
        });
    }
@Test
    public void testEntryOverflow() {
        assertThrows(IllegalArgumentException.class, () -> idx.entry(0));
    }