want a subunit-sort utility

[Martin Pool]

It would be neat if subunit could sort and collate the stream to group together the failures caused by the same root exception.

Defining 'same' is a bit complicated but if you look at Python test failures grouping by the last line (ie the exception string) would do pretty well.

[Robert Collins (lifeless)]

This is perhaps conceptually best as two filters; -group and -sort. OTOH there may be performance reasons to have -sort --group=RE instead.

I think the ideal output would still subunit, rather than (say) just the ids, so that one can immediately look at the traces, or pipe it through -ls to get the ids. OTOH this suggests potentially large buffering.

Some ways to address that:
 - spool to N temp files (one per group)
 - output a single case of a group and just enumerate the others
 - don't worry about it for now