Re: pushing for a new hash, was Re: [PATCH 2/3] rebase: Add tests for console output

Jonathan Nieder [off-list ref] writes:

2. Hard-coded object ids in tests: As Stefan hinted, many tests beyond
   t00* make assumptions about the exact values of object ids.  That's
   bad for maintainability for other reasons beyond the hash function
   transition, too.

   It should be possible to suss them out by patching git's sha1
   routine to use the ones-complement of sha1 (~sha1) instead and
   seeing which tests fail.

One particularly nasty one is t1512-rev-parse-disambiguation that
ensures that the abbreviation and disambiguation works correctly.
It uses a set of objects (tags, commits, trees and blobs) whose
object names all begin with number of "0"; which will of course
become useless once we change the hash function.

No matter what new hash function is chosen, we'd need a similar
test to ensure that disambiguation works correctly, so one of the
tasks for hash migration is to port (not drop) this test.