tests/test-absorb-phase.t

tests: add support for emitting trace events to run-tests

Right now this is pretty basic, but it's a start.

Differential Revision: https://phab.mercurial-scm.org/D4343

  $ cat >> $HGRCPATH << EOF
  > [extensions]
  > absorb=
  > drawdag=$RUNTESTDIR/drawdag.py
  > EOF

  $ hg init
  $ hg debugdrawdag <<'EOS'
  > C
  > |
  > B
  > |
  > A
  > EOS

  $ hg phase -r A --public -q
  $ hg phase -r C --secret --force -q

  $ hg update C -q
  $ printf B1 > B

  $ hg absorb -q

  $ hg log -G -T '{desc} {phase}'
  @  C secret
  |
  o  B draft
  |
  o  A public