fail.log

! t/test-sparse-files.sh  sparse restore on zfs, assuming 131072B blocks: ..... 2.629s ok
! t/test-sparse-files.sh  sparse file restore (all sparse): ...
! t/test-sparse-files.sh:44  bup restore -C restore src/latest//usr/home/sebastian/bup/t/tmp/test-sparse-files.sh-6w5JWBi/ ok
! t/test-sparse-files.sh:45  du -k -s restore                       ok
! t/test-sparse-files.sh:45  cut -f1                                ok
! t/test-! t/test-sparse-files.sh  sparse restore on zfs, assuming 131072B blocks: ..... 2.629s ok
! t/test-sparse-files.sh  sparse file restore (all sparse): ...
! t/test-sparse-files.sh:44  bup restore -C restore src/latest//usr/home/sebastian/bup/t/tmp/test-sparse-files.sh-6w5JWBi/ ok
! t/test-sparse-files.sh:45  du -k -s restore                       ok
! t/test-sparse-files.sh:45  cut -f1                                ok
! t/test-sparse-files.sh:46  [ 2 -ge 1280 ]                         FAILED
 0.491s ok

called from t/test-sparse-files.sh:46 WVPASS [ 2 -ge 1280 ]
gmake[1]: *** [Makefile:190: tmp-target-run-test-sparse-files.sh] Error 1
gmake[1]: Leaving directory '/usr/home/sebastian/bup'
! Program returned non-zero exit code (2)                           FAILED
WvTest: result code 2, total time 484.733s
./wvtest report t/tmp/test-log/*.log

! t/test-sparse-files.sh:44  bup restore -C restore src/latest//usr/home/sebastian/bup/t/tmp/test-sparse-files.sh-6w5JWBi/ ok
! t/test-sparse-files.sh:45  du -k -s restore                       ok
! t/test-sparse-files.sh:45  cut -f1                                ok
! t/test-sparse-files.sh:46  [ 2 -ge 1280 ]                         FAILED

! Program returned non-zero exit code (2)                           FAILED

WvTest: 3777 tests, 2 failures
gmake: *** [Makefile:202: test] Error 125

fs_state.txt

Apparent files size (what ls says) vs. real file size (what du says):

[sebastian@mawhrin /usr/home/sebastian/bup/t/tmp/test-sparse-files.sh-6w5JWBi]$ du -h  src/foo 
512B	src/foo
[sebastian@mawhrin /usr/home/sebastian/bup/t/tmp/test-sparse-files.sh-6w5JWBi]$ ls -alh  src/foo 
-rw-r--r--  1 sebastian  sebastian   1.3M Mar 15 16:18 src/foo
[sebastian@mawhrin /usr/home/sebastian/bup/t/tmp/test-sparse-files.sh-6w5JWBi]$ du -h restore/src/foo 
512B	restore/src/foo
[sebastian@mawhrin /usr/home/sebastian/bup/t/tmp/test-sparse-files.sh-6w5JWBi]$ ls -alh restore/src/foo 
-rw-r--r--  1 sebastian  sebastian   1.3M Mar 15 16:18 restore/src/foo

Let's ask stat:
[sebastian@mawhrin /usr/home/sebastian/bup/t/tmp/test-sparse-files.sh-6w5JWBi]$ stat src/foo 
3947765690 5291 -rw-r--r-- 1 sebastian sebastian 4294967295 1310721 "Mar 15 16:18:42 2017" "Mar 15 16:18:42 2017" "Mar 15 16:18:42 2017" "Mar 15 16:18:42 2017" 131072 1 0x800 src/foo
[sebastian@mawhrin /usr/home/sebastian/bup/t/tmp/test-sparse-files.sh-6w5JWBi]$ stat restore/src/foo 
3947765690 5304 -rw-r--r-- 1 sebastian sebastian 4294967295 1310721 "Mar 15 16:18:42 2017" "Mar 15 16:18:42 2017" "Mar 15 16:18:45 2017" "Mar 15 16:18:45 2017" 131072 1 0x800 restore/src/foo

=> Restore seems to have worked fine

Let's play with du:
[sebastian@mawhrin /usr/home/sebastian/bup/t/tmp/test-sparse-files.sh-6w5JWBi]$ du -s -k restore/
2	restore/
[sebastian@mawhrin /usr/home/sebastian/bup/t/tmp/test-sparse-files.sh-6w5JWBi]$ du -s -k src/    
1	src/
[sebastian@mawhrin /usr/home/sebastian/bup/t/tmp/test-sparse-files.sh-6w5JWBi]$ du -s -k src/*
1	src/foo
[sebastian@mawhrin /usr/home/sebastian/bup/t/tmp/test-sparse-files.sh-6w5JWBi]$ du -s -k restore/*
1	restore/src
[sebastian@mawhrin /usr/home/sebastian/bup/t/tmp/test-sparse-files.sh-6w5JWBi]$ du -s -k restore/src/*
1	restore/src/foo

[sebastian@mawhrin /usr/home/sebastian/bup/t/tmp/test-sparse-files.sh-6w5JWBi]$ du -h src/
1.0K	src/
[sebastian@mawhrin /usr/home/sebastian/bup/t/tmp/test-sparse-files.sh-6w5JWBi]$ du -h restore/
1.0K	restore/src
1.5K	restore/
[sebastian@mawhrin /usr/home/sebastian/bup/t/tmp/test-sparse-files.sh-6w5JWBi]$ du -h restore/src/
1.0K	restore/src/

Problem.txt

Looking at https://github.com/bup/bup/blob/master/t/test-sparse-files.sh#L46
restore_size=$(WVPASS du -k -s restore | WVPASS cut -f1) || exit $?
WVPASS [ "$restore_size" -ge "$((data_size / 1024))" ]

For a block size of 4096 bytes:
data_size = block_size * 10 = 40960

File is created using:
WVPASS dd if=/dev/zero of=src/foo seek="$data_size" bs=1 count=1

restore_size = 4 (a single block if we have sparse file support)

This leads to:
WVPASS [ "4" -ge "40" ]

Which should never pass for any sensible blocksize ...