In the darcs darcs repository, I did something like (darcs push staging; darcs
check --repodir=staging --test) twice.

The first time, the test failed because of some pre-requisites not being met,
and the second time, I got this error message:

Missing items in index!
  .boring
  tests/remove.sh
  tests/issue1224_convert-darcs2-repository.sh
  tests/issue1636-match-hunk.sh

Hash mismatch(es)!
tests/remove.sh
    index: 
  working: 6be3b2a72670171b29f1243bede2ac73961ab73bb465d3a07e8f179be8536313
tests/issue1636-match-hunk.sh
    index: 
  working: 657a73965c8726b4562170994e1ee8e2ef4ad7c70a8c066a1515223977b9aafd
tests/issue1224_convert-darcs2-repository.sh
    index: 
  working: 7a7119d5dbf5fe147653e70143afa631966c1b3dbdf41fdd2d6425f54ff8f4c1
tests
    index: 0e5a8d36e709c258eee4c46d0f318cc7e371f23232c3e34004d7afdfbd5cfb43
  working: b89c7e24e6eacf5521148dfa3c73b140ca56dc58c95664da98971d4d7fb3f059
.boring
    index: 
  working: 12bfba1b0856efb56ff4b88cafa78ed4e2f37b7626675b7c61deed8575edd88b

Bad index.

I discussed the issue with Petr here:
http://irclog.perlgeek.de/darcs/2009-12-02#i_1791325

who has isolated the problem to the fact that the darcs check test happens
before the index check (please correct me if I'm wrong, Petr).  He says "what
happens is that we invalidateIndex in Apply, but not necessarily at the right spot"

So, it looks like it's just a matter of coding to fix this.

Yay for dog-fooding!

I have no idea how to reproduce this. A few tries with add, apply --test and a 
failing test did not lead to any corruption. I don't completely understand what 
your posthook and test do... Is it the case that you run apply --test, or that 
you run apply post-hook darcs check? The latter case looks rather suspicious, 
but I haven't tried it yet. With apply --test, the patches are not applied at 
all when the test fails. I'll need more data (ideally a reproducible testcase).

It's check --test that I'm running, I think...

See http://gist.github.com/247253

We'd need to be able to reproduce the bad apply, but there are two variables here:

- which patches was I trying to push
- and what (likely unstable) version of Darcs was I trying to do the apply with

Oh well, I guess this is dead.  The good news is that thinking about this has
caused Petr to uncover a new bug... it'd be good if he could post it :-)