tests/test-push-checkheads-partial-C3.t

tests: handle string escaping/encoding on Python 3

This code was failing on Python 3 for a few reasons:

1) sys.argv is str and str doesn't have a .decode()
2) the "string_escape" encoding was renamed to "unicode_escape"

It is wonky casting to bytes to str to bytes. But this is test
code, so meh. I don't believe we exercise any code paths in these
tests where the arguments aren't ascii.

Differential Revision: https://phab.mercurial-scm.org/D5667

====================================
Testing head checking code: Case C-3
====================================

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 C: case were the branch is only partially obsoleted
TestCase 3: 2 changeset branch, only the head is pruned

.. old-state:
..
.. * 2 changeset branch
..
.. new-state:
..
.. * old head is pruned
.. * 1 new unrelated branch
..
.. expected-result:
..
.. * push denied
..
.. graph-summary:
..
..   B ⊗
..     |
..   A ◔ ◔ C
..     |/
..     ●

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

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

  $ mkdir C3
  $ cd C3
  $ setuprepos
  creating basic server and client repo
  updating to branch default
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cd server
  $ mkcommit B0
  $ cd ../client
  $ hg pull
  pulling from $TESTTMP/C3/server
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files
  new changesets d73caddc5533 (1 drafts)
  (run 'hg update' to get a working copy)
  $ hg up 0
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
  $ mkcommit C0
  created new head
  $ hg debugobsolete --record-parents `getid "desc(B0)"`
  obsoleted 1 changesets
  $ hg log -G --hidden
  @  0f88766e02d6 (draft): C0
  |
  | x  d73caddc5533 (draft): B0
  | |
  | o  8aaa48160adc (draft): A0
  |/
  o  1e4be0697311 (public): root
  

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

  $ hg push
  pushing to $TESTTMP/C3/server
  searching for changes
  abort: push creates new remote head 0f88766e02d6!
  (merge or see 'hg help push' for details about pushing new heads)
  [255]

  $ cd ../..