not ok 3 - fileref_create chunksize=0 'a-aa' works (2 sha1 blobrefs)

[garlick]

Problem: some sparse file fileref unit tests fail on Debian 12 tmpfs:

ok 1 - fileref_create chunksize=0 'aaaa' works (1 sha1 blobrefs)
ok 2 - fileref_create chunksize=0 '-aaa' works (1 sha1 blobrefs)
# fileref.blobvec has incorrect length (expected 2 got 1)
not ok 3 - fileref_create chunksize=0 'a-aa' works (2 sha1 blobrefs)
#   Failed test 'fileref_create chunksize=0 'a-aa' works (2 sha1 blobrefs)'
#   at test/fileref.c line 489.
ok 4 - fileref_create chunksize=0 'aaa-' works (1 sha1 blobrefs)
ok 5 - fileref_create chunksize=0 '----' works (0 sha1 blobrefs)
# fileref.blobvec has incorrect length (expected 3 got 1)
not ok 6 - fileref_create chunksize=0 'ac-e--f-' works (3 sha1 blobrefs)
#   Failed test 'fileref_create chunksize=0 'ac-e--f-' works (3 sha1 blobrefs)'
#   at test/fileref.c line 489.
ok 7 - fileref_create chunksize=5500 'aaaa' works (3 sha1 blobrefs)
ok 8 - fileref_create chunksize=8192 'aaaa' works (2 sha1 blobrefs)
ok 9 - fileref_create chunksize=16384 'aaaa' works (1 sha1 blobrefs)
# fileref.blobvec has incorrect length (expected 2 got 4)
not ok 10 - fileref_create chunksize=4096 'a--a' works (2 sha1 blobrefs)
#   Failed test 'fileref_create chunksize=4096 'a--a' works (2 sha1 blobrefs)'
#   at test/fileref.c line 489.
# fileref.blobvec has incorrect length (expected 2 got 4)
not ok 11 - fileref_create chunksize=5000 'a--a' works (2 sha1 blobrefs)
#   Failed test 'fileref_create chunksize=5000 'a--a' works (2 sha1 blobrefs)'
#   at test/fileref.c line 489.
# fileref.blobvec has incorrect length (expected 4 got 6)
not ok 12 - fileref_create chunksize=3000 'a--a' works (4 sha256 blobrefs)
#   Failed test 'fileref_create chunksize=3000 'a--a' works (4 sha256 blobrefs)'
#   at test/fileref.c line 489.

These tests are skipped if the file system does not support sparse files, but that check passes in this case.

I suppose the decision of whether to preserve the sparseness is really up to the file system so the test is inherently fragile.