tests/test-nested-repo.t

context: introduce the nullsub() method

Ultimately, this will be used by scmutil.  The subrepo module already imports
it, so it can't import the subrepo module to access the underlying method.

  $ hg init a
  $ cd a
  $ hg init b
  $ echo x > b/x

Should print nothing:

  $ hg add b
  $ hg st

  $ echo y > b/y
  $ hg st

Should fail:

  $ hg st b/x
  abort: path 'b/x' is inside nested repo 'b' (glob)
  [255]
  $ hg add b/x
  abort: path 'b/x' is inside nested repo 'b' (glob)
  [255]

Should fail:

  $ hg add b b/x
  abort: path 'b/x' is inside nested repo 'b' (glob)
  [255]
  $ hg st

Should arguably print nothing:

  $ hg st b

  $ echo a > a
  $ hg ci -Ama a

Should fail:

  $ hg mv a b
  abort: path 'b/a' is inside nested repo 'b' (glob)
  [255]
  $ hg st

  $ cd ..