Test Failing: Computer Too Fast

A peculiar bugToday I fixed a very interesting bug. The code reads //Segment lineage entries are sorted in chronological order by lineageEntries.entrySet() .stream() .sorted(Map.Entry.comparingByValue( Comparator.comparingLong(LineageEntry::getTimestamp) )); The test creates two LineageEntry, then prints them, and ensures they are sorted by time of creation — that is to say the first one created is printed before the second one. It works fine most of the time.... Except on a computer that is just too fast. Two consecutive LineageEntry can be created within a millisecond and therefore have the same timestamp! And here's the problem... the ordering of LineageEntry with identical timestamps is undefined. The test fails 50% of the time. The fix is trivial: Add a secondary sort order. The ordering didn't even matter all that much: it is just how the log statement is ordering entries. We want it to be sorted by time, though, and then, I think it is better that entries within a timestamp are…