tests/test-worker.t

bundle: allow bundle command to use changegroup3 in tests

Since bundle2 writes changegroup version, we can just reuse the bundle2
format for changegroup3.

This won't enable the bundle command to write changegroup3 in the wild,
since exchange.parsebundlespec only returns changegroup2. It unlocks tests
to override exchange.parsebundlespec and get "hg bundle" write changegroup3.

Test UI worker interaction

  $ cat > t.py <<EOF
  > from __future__ import absolute_import, print_function
  > from mercurial import (
  >     cmdutil,
  >     ui as uimod,
  >     worker,
  > )
  > def runme(ui, args):
  >     for arg in args:
  >         ui.status('run\n')
  >         yield 1, arg
  > cmdtable = {}
  > command = cmdutil.command(cmdtable)
  > @command('test', [], 'hg test [COST]')
  > def t(ui, repo, cost=1.0):
  >     cost = float(cost)
  >     ui.status('start\n')
  >     runs = worker.worker(ui, cost, runme, (ui,), range(8))
  >     for n, i in runs:
  >         pass
  >     ui.status('done\n')
  > EOF
  $ abspath=`pwd`/t.py
  $ hg init

Run tests with worker enable by forcing a heigh cost

  $ hg --config "extensions.t=$abspath" test 100000.0
  start
  run
  run
  run
  run
  run
  run
  run
  run
  done

Run tests without worker by forcing a low cost

  $ hg --config "extensions.t=$abspath" test 0.0000001
  start
  run
  run
  run
  run
  run
  run
  run
  run
  done