tests/test-revert-unknown.t

import-checkers: split tests of the tool from running it on the source

We did such splits for other tools already. The 'test-check-*.t' performs the
check of the source code while the regular tests verifies the tools works.

One of the benefit is that is provides a simple file to reuse in third party
extensions.

  $ hg init
  $ touch unknown

  $ touch a
  $ hg add a
  $ hg ci -m "1"

  $ touch b
  $ hg add b
  $ hg ci -m "2"

Should show unknown

  $ hg status
  ? unknown
  $ hg revert -r 0 --all
  removing b

Should show unknown and b removed

  $ hg status
  R b
  ? unknown

Should show a and unknown

  $ ls
  a
  unknown