tests/test-push-checkheads-superceed-A8.t

tests: avoid referring to pvec in demandimport test

Nothing else currently uses pvec, so we may want to delete it (but
Augie Fackler says he may want to use it). To enable deletion, this
patch replaces it by the error module in the demandimport test (any
module works). However, since the error module had already been loaded
at this point in the test (via the util module), I moved it earlier in
the test so it's still not loaded (although I'm not sure if that's
even relevant to the test).

Differential Revision: https://phab.mercurial-scm.org/D2287

====================================
Testing head checking code: Case A-8
====================================

Mercurial checks for the introduction of new heads on push. Evolution comes
into play to detect if existing branches on the server are being replaced by
some of the new one we push.

This case is part of a series of tests checking this behavior.

Category A: simple case involving a branch being superceeded by another.
TestCase 8: single-changeset branch indirect rewrite

.. old-state:
..
.. * 1-changeset branch
..
.. new-state:
..
.. * 1-changeset branch succeeding to A, through another unpushed changesets
..
.. expected-result:
..
.. * push allowed
..
.. graph-summary:
..
..       A'
..   A ø⇠ø⇠◔ A''
..     |/ /
..     | /
..     |/
..     ●

  $ . $TESTDIR/testlib/push-checkheads-util.sh

Test setup
----------

  $ mkdir A8
  $ cd A8
  $ setuprepos
  creating basic server and client repo
  updating to branch default
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cd client
  $ hg up 0
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
  $ mkcommit A1
  created new head
  $ hg up 0
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
  $ mkcommit A2
  created new head
  $ hg debugobsolete `getid "desc(A0)" ` `getid "desc(A1)"`
  obsoleted 1 changesets
  $ hg debugobsolete `getid "desc(A1)" ` `getid "desc(A2)"`
  obsoleted 1 changesets
  $ hg log -G --hidden
  @  c1f8d089020f (draft): A2
  |
  | x  f6082bc4ffef (draft): A1
  |/
  | x  8aaa48160adc (draft): A0
  |/
  o  1e4be0697311 (public): root
  

Actual testing
--------------

  $ hg push
  pushing to $TESTTMP/A8/server
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files (+1 heads)
  2 new obsolescence markers
  obsoleted 1 changesets

  $ cd ../..