tests/test-revisions.t

branchcache: do not accept "empty update"

This currently does not happens and it will be simpler that is remains that way.
If all update do something, we will be able to simply declare, in a later
changesets, that all update to result in a dirty branchcache.

  $ hg init repo
  $ cd repo

  $ echo 0 > a
  $ hg ci -qAm 0
  $ for i in 5 8 14 43 167; do
  >   hg up -q 0
  >   echo $i > a
  >   hg ci -qm $i
  > done
  $ cat <<EOF >> .hg/hgrc
  > [alias]
  > l = log -T '{rev}:{shortest(node,1)}\n'
  > EOF

  $ hg l
  5:00f
  4:7ba5d
  3:7ba57
  2:72
  1:9
  0:b
  $ cat <<EOF >> .hg/hgrc
  > [experimental]
  > revisions.disambiguatewithin=not 4
  > EOF
  $ hg l
  5:00
  4:7ba5d
  3:7b
  2:72
  1:9
  0:b
9 was unambiguous and still is
  $ hg l -r 9
  1:9
7 was ambiguous and still is
  $ hg l -r 7
  abort: ambiguous revision identifier: 7
  [10]
7b is no longer ambiguous
  $ hg l -r 7b
  3:7b

  $ cd ..