tests/test-xdg.t

branchmap: Add a test about writing branchmap and aborted transaction

It turn out that we update the branchmap on disk whenever we recompute it…
including in a middle of a transaction. This means writing the new branchmap too
early (the changeset are not visible yet) and worse… it mean writing branchmap
for transaction we rollback.

so we introduce a test to highlight the issue (and prevent it to regress in the
future).

Differential Revision: https://phab.mercurial-scm.org/D12126

#if no-windows no-osx

  $ mkdir -p xdgconf/hg
  $ echo '[ui]' > xdgconf/hg/hgrc
  $ echo 'username = foobar' >> xdgconf/hg/hgrc
  $ XDG_CONFIG_HOME="`pwd`/xdgconf" ; export XDG_CONFIG_HOME
  $ unset HGRCPATH
  $ hg config ui.username 2>/dev/null
  foobar

#endif